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-<table class="head">
-  <tr>
-    <td class="head-ltitle">HWPMC(4)</td>
-    <td class="head-vol">Device Drivers Manual</td>
-    <td class="head-rtitle">HWPMC(4)</td>
-  </tr>
-</table>
-<div class="manual-text">
-<section class="Sh">
-<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
-<p class="Pp"><code class="Nm">hwpmc</code> &#x2014; <span class="Nd">Hardware
-    Performance Monitoring Counter support</span></p>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
-<p class="Pp">The following option must be present in the kernel configuration
-    file:</p>
-<div class="Bd Pp Bd-indent"><code class="Cd">options HWPMC_HOOKS</code></div>
-<p class="Pp">Additionally, for i386 systems:</p>
-<div class="Bd Pp Bd-indent"><code class="Cd">device apic</code></div>
-<p class="Pp">To load the driver as a module at boot time:</p>
-<div class="Bd Pp Bd-indent Li">
-<pre>sysrc kld_list+=hwpmc</pre>
-</div>
-<p class="Pp">Alternatively, to compile the driver into the kernel:</p>
-<div class="Bd Pp Bd-indent"><code class="Cd">device hwpmc</code></div>
-<p class="Pp">To enable debugging features (see
-    <a class="Sx" href="#DEBUGGING">DEBUGGING</a>):</p>
-<div class="Bd Pp Bd-indent"><code class="Cd">options KTR</code>
-<br/>
-<code class="Cd">options KTR_COMPILE=(KTR_SUBSYS)</code>
-<br/>
-<code class="Cd">options KTR_MASK=(KTR_SUBSYS)</code>
-<br/>
-<code class="Cd">options HWPMC_DEBUG</code></div>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
-<p class="Pp">The <code class="Nm">hwpmc</code> driver virtualizes the hardware
-    performance monitoring facilities in modern CPUs and provides support for
-    using these facilities from user level processes.</p>
-<p class="Pp">The driver supports multi-processor systems.</p>
-<p class="Pp">PMCs are allocated using the
-    <code class="Dv">PMC_OP_PMCALLOCATE</code> request. A successful
-    <code class="Dv">PMC_OP_PMCALLOCATE</code> request will return a handle to
-    the requesting process. Subsequent operations on the allocated PMC use this
-    handle to denote the specific PMC. A process that has successfully allocated
-    a PMC is termed an &#x201C;owner process&#x201D;.</p>
-<p class="Pp">PMCs may be allocated with process or system scope.</p>
-<dl class="Bl-tag">
-  <dt id="Process-scope"><a class="permalink" href="#Process-scope"><i class="Em">Process-scope</i></a></dt>
-  <dd>The PMC is active only when a thread belonging to a process it is attached
-      to is scheduled on a CPU.</dd>
-  <dt id="System-scope"><a class="permalink" href="#System-scope"><i class="Em">System-scope</i></a></dt>
-  <dd>The PMC operates independently of processes and measures hardware events
-      for the system as a whole.</dd>
-</dl>
-<p class="Pp">PMCs may be allocated for counting or for sampling:</p>
-<dl class="Bl-tag">
-  <dt id="Counting"><a class="permalink" href="#Counting"><i class="Em">Counting</i></a></dt>
-  <dd>In counting modes, the PMCs count hardware events. These counts are
-      retrievable using the <code class="Dv">PMC_OP_PMCREAD</code> system call
-      on all architectures. Some architectures offer faster methods of reading
-      these counts.</dd>
-  <dt id="Sampling"><a class="permalink" href="#Sampling"><i class="Em">Sampling</i></a></dt>
-  <dd>In sampling modes, the PMCs are configured to sample the CPU instruction
-      pointer (and optionally to capture the call chain leading up to the
-      sampled instruction pointer) after a configurable number of hardware
-      events have been observed. Instruction pointer samples and call chain
-      records are usually directed to a log file for subsequent analysis.</dd>
-</dl>
-<p class="Pp">Scope and operational mode are orthogonal; a PMC may thus be
-    configured to operate in one of the following four modes:</p>
-<dl class="Bl-tag">
-  <dt>Process-scope, counting</dt>
-  <dd>These PMCs count hardware events whenever a thread in their attached
-      process is scheduled on a CPU. These PMCs normally count from zero, but
-      the initial count may be set using the
-      <code class="Dv">PMC_OP_SETCOUNT</code> operation. Applications can read
-      the value of the PMC anytime using the
-      <code class="Dv">PMC_OP_PMCRW</code> operation.</dd>
-  <dt>Process-scope, sampling</dt>
-  <dd>These PMCs sample the target processes instruction pointer after they have
-      seen the configured number of hardware events. The PMCs only count events
-      when a thread belonging to their attached process is active. The desired
-      frequency of sampling is set using the
-      <code class="Dv">PMC_OP_SETCOUNT</code> operation prior to starting the
-      PMC. Log files are configured using the
-      <code class="Dv">PMC_OP_CONFIGURELOG</code> operation.</dd>
-  <dt>System-scope, counting</dt>
-  <dd>These PMCs count hardware events seen by them independent of the processes
-      that are executing. The current count on these PMCs can be read using the
-      <code class="Dv">PMC_OP_PMCRW</code> request. These PMCs normally count
-      from zero, but the initial count may be set using the
-      <code class="Dv">PMC_OP_SETCOUNT</code> operation.</dd>
-  <dt>System-scope, sampling</dt>
-  <dd>These PMCs will periodically sample the instruction pointer of the CPU
-      they are allocated on, and will write the sample to a log for further
-      processing. The desired frequency of sampling is set using the
-      <code class="Dv">PMC_OP_SETCOUNT</code> operation prior to starting the
-      PMC. Log files are configured using the
-      <code class="Dv">PMC_OP_CONFIGURELOG</code> operation.
-    <p class="Pp">System-wide statistical sampling can only be enabled by a
-        process with super-user privileges.</p>
-  </dd>
-</dl>
-<p class="Pp">Processes are allowed to allocate as many PMCs as the hardware and
-    current operating conditions permit. Processes may mix allocations of
-    system-wide and process-private PMCs. Multiple processes may be using PMCs
-    simultaneously.</p>
-<p class="Pp">Allocated PMCs are started using the
-    <code class="Dv">PMC_OP_PMCSTART</code> operation, and stopped using the
-    <code class="Dv">PMC_OP_PMCSTOP</code> operation. Stopping and starting a
-    PMC is permitted at any time the owner process has a valid handle to the
-    PMC.</p>
-<p class="Pp">Process-private PMCs need to be attached to a target process
-    before they can be used. Attaching a process to a PMC is done using the
-    <code class="Dv">PMC_OP_PMCATTACH</code> operation. An already attached PMC
-    may be detached from its target process using the converse
-    <code class="Dv">PMC_OP_PMCDETACH</code> operation. Issuing a
-    <code class="Dv">PMC_OP_PMCSTART</code> operation on an as yet unattached
-    PMC will cause it to be attached to its owner process. The following rules
-    determine whether a given process may attach a PMC to another target
-    process:</p>
-<ul class="Bl-bullet Bl-compact">
-  <li>A non-jailed process with super-user privileges is allowed to attach to
-      any other process in the system.</li>
-  <li>Other processes are only allowed to attach to targets that they would be
-      able to attach to for debugging (as determined by
-      <a class="Xr">p_candebug(9)</a>).</li>
-</ul>
-<p class="Pp">PMCs are released using <code class="Dv">PMC_OP_PMCRELEASE</code>.
-    After a successful <code class="Dv">PMC_OP_PMCRELEASE</code> operation the
-    handle to the PMC will become invalid.</p>
-<section class="Ss">
-<h2 class="Ss" id="Modifier_Flags"><a class="permalink" href="#Modifier_Flags">Modifier
-  Flags</a></h2>
-<p class="Pp">The <code class="Dv">PMC_OP_PMCALLOCATE</code> operation supports
-    the following flags that modify the behavior of an allocated PMC:</p>
-<dl class="Bl-tag">
-  <dt id="PMC_F_CALLCHAIN"><a class="permalink" href="#PMC_F_CALLCHAIN"><code class="Dv">PMC_F_CALLCHAIN</code></a></dt>
-  <dd>This modifier informs sampling PMCs to record a callchain when capturing a
-      sample. The maximum depth to which call chains are recorded is specified
-      by the <var class="Va">kern.hwpmc.callchaindepth</var> kernel
-    tunable.</dd>
-  <dt id="PMC_F_DESCENDANTS"><a class="permalink" href="#PMC_F_DESCENDANTS"><code class="Dv">PMC_F_DESCENDANTS</code></a></dt>
-  <dd>This modifier is valid only for a PMC being allocated in process-private
-      mode. It signifies that the PMC will track hardware events for its target
-      process and the target's current and future descendants.</dd>
-  <dt id="PMC_F_LOG_PROCCSW"><a class="permalink" href="#PMC_F_LOG_PROCCSW"><code class="Dv">PMC_F_LOG_PROCCSW</code></a></dt>
-  <dd>This modifier is valid only for a PMC being allocated in process-private
-      mode. When this modifier is present, at every context switch,
-      <code class="Nm">hwpmc</code> will log a record containing the number of
-      hardware events seen by the target process when it was scheduled on the
-      CPU.</dd>
-  <dt id="PMC_F_LOG_PROCEXIT"><a class="permalink" href="#PMC_F_LOG_PROCEXIT"><code class="Dv">PMC_F_LOG_PROCEXIT</code></a></dt>
-  <dd>This modifier is valid only for a PMC being allocated in process-private
-      mode. With this modifier present, <code class="Nm">hwpmc</code> will
-      maintain per-process counts for each target process attached to a PMC. At
-      process exit time, a record containing the target process' PID and the
-      accumulated per-process count for that process will be written to the
-      configured log file.</dd>
-</dl>
-<p class="Pp">Modifiers <code class="Dv">PMC_F_LOG_PROCEXIT</code> and
-    <code class="Dv">PMC_F_LOG_PROCCSW</code> may be used in combination with
-    modifier <code class="Dv">PMC_F_DESCENDANTS</code> to track the behavior of
-    complex pipelines of processes. PMCs with modifiers
-    <code class="Dv">PMC_F_LOG_PROCEXIT</code> and
-    <code class="Dv">PMC_F_LOG_PROCCSW</code> cannot be started until their
-    owner process has configured a log file.</p>
-</section>
-<section class="Ss">
-<h2 class="Ss" id="Signals"><a class="permalink" href="#Signals">Signals</a></h2>
-<p class="Pp">The <code class="Nm">hwpmc</code> driver may deliver signals to
-    processes that have allocated PMCs:</p>
-<dl class="Bl-tag">
-  <dt id="SIGIO"><a class="permalink" href="#SIGIO"><code class="Dv">SIGIO</code></a></dt>
-  <dd>A <code class="Dv">PMC_OP_PMCRW</code> operation was attempted on a
-      process-private PMC that does not have attached target processes.</dd>
-  <dt id="SIGBUS"><a class="permalink" href="#SIGBUS"><code class="Dv">SIGBUS</code></a></dt>
-  <dd>The <code class="Nm">hwpmc</code> driver is being unloaded from the
-      kernel.</dd>
-</dl>
-</section>
-<section class="Ss">
-<h2 class="Ss" id="PMC_ROW_DISPOSITIONS"><a class="permalink" href="#PMC_ROW_DISPOSITIONS">PMC
-  ROW DISPOSITIONS</a></h2>
-<p class="Pp">A PMC row is defined as the set of PMC resources at the same
-    hardware address in the CPUs in a system. Since process scope PMCs need to
-    move between CPUs following their target threads, allocation of a process
-    scope PMC reserves all PMCs in a PMC row for use only with process scope
-    PMCs. Accordingly a PMC row will be in one of the following
-  dispositions:</p>
-<dl class="Bl-tag Bl-compact">
-  <dt id="PMC_DISP_FREE"><a class="permalink" href="#PMC_DISP_FREE"><code class="Dv">PMC_DISP_FREE</code></a></dt>
-  <dd>Hardware counters in this row are free and may be use to satisfy either of
-      system scope or process scope allocation requests.</dd>
-  <dt id="PMC_DISP_THREAD"><a class="permalink" href="#PMC_DISP_THREAD"><code class="Dv">PMC_DISP_THREAD</code></a></dt>
-  <dd>Hardware counters in this row are in use by process scope PMCs and are
-      only available for process scope allocation requests.</dd>
-  <dt id="PMC_DISP_STANDALONE"><a class="permalink" href="#PMC_DISP_STANDALONE"><code class="Dv">PMC_DISP_STANDALONE</code></a></dt>
-  <dd>Some hardware counters in this row have been administratively disabled or
-      are in use by system scope PMCs. Non-disabled hardware counters in such a
-      row may be used for satisfying system scope allocation requests. No
-      process scope PMCs will use hardware counters in this row.</dd>
-</dl>
-</section>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="COMPATIBILITY"><a class="permalink" href="#COMPATIBILITY">COMPATIBILITY</a></h1>
-<p class="Pp">The API and ABI documented in this manual page may change in the
-    future. This interface is intended to be consumed by the
-    <a class="Xr">pmc(3)</a> library; other consumers are unsupported.
-    Applications targeting PMCs should use the <a class="Xr">pmc(3)</a> library
-    API.</p>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="PROGRAMMING_API"><a class="permalink" href="#PROGRAMMING_API">PROGRAMMING
-  API</a></h1>
-<p class="Pp">The <code class="Nm">hwpmc</code> driver operates using a system
-    call number that is dynamically allotted to it when it is loaded into the
-    kernel.</p>
-<p class="Pp">The <code class="Nm">hwpmc</code> driver supports the following
-    operations:</p>
-<dl class="Bl-tag">
-  <dt id="PMC_OP_CONFIGURELOG"><a class="permalink" href="#PMC_OP_CONFIGURELOG"><code class="Dv">PMC_OP_CONFIGURELOG</code></a></dt>
-  <dd>Configure a log file for PMCs that require a log file. The
-      <code class="Nm">hwpmc</code> driver will write log data to this file
-      asynchronously. If it encounters an error, logging will be stopped and the
-      error code encountered will be saved for subsequent retrieval by a
-      <code class="Dv">PMC_OP_FLUSHLOG</code> request.</dd>
-  <dt id="PMC_OP_FLUSHLOG"><a class="permalink" href="#PMC_OP_FLUSHLOG"><code class="Dv">PMC_OP_FLUSHLOG</code></a></dt>
-  <dd>Transfer buffered log data inside <code class="Nm">hwpmc</code> to a
-      configured output file. This operation returns to the caller after the
-      write operation has returned. The returned error code reflects any pending
-      error state inside <code class="Nm">hwpmc</code>.</dd>
-  <dt id="PMC_OP_GETCAPS"><a class="permalink" href="#PMC_OP_GETCAPS"><code class="Dv">PMC_OP_GETCAPS</code></a></dt>
-  <dd>Retrieve the capabilities associated with a specific PMC counter. Some
-      capabilities may be limited to specific indices (i.e., not available
-      across all counters within a class).</dd>
-  <dt id="PMC_OP_GETCPUINFO"><a class="permalink" href="#PMC_OP_GETCPUINFO"><code class="Dv">PMC_OP_GETCPUINFO</code></a></dt>
-  <dd>Retrieve information about the highest possible CPU number for the system,
-      and the number of hardware performance monitoring counters available per
-      CPU.</dd>
-  <dt id="PMC_OP_GETDRIVERSTATS"><a class="permalink" href="#PMC_OP_GETDRIVERSTATS"><code class="Dv">PMC_OP_GETDRIVERSTATS</code></a></dt>
-  <dd>Retrieve module statistics (for analyzing the behavior of
-      <code class="Nm">hwpmc</code> itself).</dd>
-  <dt id="PMC_OP_GETMODULEVERSION"><a class="permalink" href="#PMC_OP_GETMODULEVERSION"><code class="Dv">PMC_OP_GETMODULEVERSION</code></a></dt>
-  <dd>Retrieve the version number of API.</dd>
-  <dt id="PMC_OP_GETPMCINFO"><a class="permalink" href="#PMC_OP_GETPMCINFO"><code class="Dv">PMC_OP_GETPMCINFO</code></a></dt>
-  <dd>Retrieve information about the current state of the PMCs on a given
-    CPU.</dd>
-  <dt id="PMC_OP_PMCADMIN"><a class="permalink" href="#PMC_OP_PMCADMIN"><code class="Dv">PMC_OP_PMCADMIN</code></a></dt>
-  <dd>Set the administrative state (i.e., whether enabled or disabled) for the
-      hardware PMCs managed by the <code class="Nm">hwpmc</code> driver. The
-      invoking process needs to possess the
-      <code class="Dv">PRIV_PMC_MANAGE</code> privilege.</dd>
-  <dt id="PMC_OP_PMCALLOCATE"><a class="permalink" href="#PMC_OP_PMCALLOCATE"><code class="Dv">PMC_OP_PMCALLOCATE</code></a></dt>
-  <dd>Allocate and configure a PMC. On successful allocation, a handle to the
-      PMC (a 32 bit value) is returned.</dd>
-  <dt id="PMC_OP_PMCATTACH"><a class="permalink" href="#PMC_OP_PMCATTACH"><code class="Dv">PMC_OP_PMCATTACH</code></a></dt>
-  <dd>Attach a process mode PMC to a target process. The PMC will be active
-      whenever a thread in the target process is scheduled on a CPU.
-    <p class="Pp">If the <code class="Dv">PMC_F_DESCENDANTS</code> flag had been
-        specified at PMC allocation time, then the PMC is attached to all
-        current and future descendants of the target process.</p>
-  </dd>
-  <dt id="PMC_OP_PMCDETACH"><a class="permalink" href="#PMC_OP_PMCDETACH"><code class="Dv">PMC_OP_PMCDETACH</code></a></dt>
-  <dd>Detach a PMC from its target process.</dd>
-  <dt id="PMC_OP_PMCRELEASE"><a class="permalink" href="#PMC_OP_PMCRELEASE"><code class="Dv">PMC_OP_PMCRELEASE</code></a></dt>
-  <dd>Release a PMC.</dd>
-  <dt id="PMC_OP_PMCRW"><a class="permalink" href="#PMC_OP_PMCRW"><code class="Dv">PMC_OP_PMCRW</code></a></dt>
-  <dd>Read and write a PMC. This operation is valid only for PMCs configured in
-      counting modes.</dd>
-  <dt id="PMC_OP_SETCOUNT"><a class="permalink" href="#PMC_OP_SETCOUNT"><code class="Dv">PMC_OP_SETCOUNT</code></a></dt>
-  <dd>Set the initial count (for counting mode PMCs) or the desired sampling
-      rate (for sampling mode PMCs).</dd>
-  <dt id="PMC_OP_PMCSTART"><a class="permalink" href="#PMC_OP_PMCSTART"><code class="Dv">PMC_OP_PMCSTART</code></a></dt>
-  <dd>Start a PMC.</dd>
-  <dt id="PMC_OP_PMCSTOP"><a class="permalink" href="#PMC_OP_PMCSTOP"><code class="Dv">PMC_OP_PMCSTOP</code></a></dt>
-  <dd>Stop a PMC.</dd>
-  <dt id="PMC_OP_WRITELOG"><a class="permalink" href="#PMC_OP_WRITELOG"><code class="Dv">PMC_OP_WRITELOG</code></a></dt>
-  <dd>Insert a timestamped user record into the log file.</dd>
-</dl>
-<section class="Ss">
-<h2 class="Ss" id="i386_Specific_API"><a class="permalink" href="#i386_Specific_API">i386
-  Specific API</a></h2>
-<p class="Pp">Some i386 family CPUs support the RDPMC instruction which allows a
-    user process to read a PMC value without needing to invoke a
-    <code class="Dv">PMC_OP_PMCRW</code> operation. On such CPUs, the machine
-    address associated with an allocated PMC is retrievable using the
-    <code class="Dv">PMC_OP_PMCX86GETMSR</code> system call.</p>
-<dl class="Bl-tag">
-  <dt id="PMC_OP_PMCX86GETMSR"><a class="permalink" href="#PMC_OP_PMCX86GETMSR"><code class="Dv">PMC_OP_PMCX86GETMSR</code></a></dt>
-  <dd>Retrieve the MSR (machine specific register) number associated with the
-      given PMC handle.
-    <p class="Pp">The PMC needs to be in process-private mode and allocated
-        without the <code class="Dv">PMC_F_DESCENDANTS</code> modifier flag, and
-        should be attached only to its owner process at the time of the
-      call.</p>
-  </dd>
-</dl>
-</section>
-<section class="Ss">
-<h2 class="Ss" id="amd64_Specific_API"><a class="permalink" href="#amd64_Specific_API">amd64
-  Specific API</a></h2>
-<p class="Pp">AMD64 CPUs support the RDPMC instruction which allows a user
-    process to read a PMC value without needing to invoke a
-    <code class="Dv">PMC_OP_PMCRW</code> operation. The machine address
-    associated with an allocated PMC is retrievable using the
-    <code class="Dv">PMC_OP_PMCX86GETMSR</code> system call.</p>
-<dl class="Bl-tag">
-  <dt id="PMC_OP_PMCX86GETMSR~2"><a class="permalink" href="#PMC_OP_PMCX86GETMSR~2"><code class="Dv">PMC_OP_PMCX86GETMSR</code></a></dt>
-  <dd>Retrieve the MSR (machine specific register) number associated with the
-      given PMC handle.
-    <p class="Pp">The PMC needs to be in process-private mode and allocated
-        without the <code class="Dv">PMC_F_DESCENDANTS</code> modifier flag, and
-        should be attached only to its owner process at the time of the
-      call.</p>
-  </dd>
-</dl>
-</section>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="SYSCTL_VARIABLES_AND_LOADER_TUNABLES"><a class="permalink" href="#SYSCTL_VARIABLES_AND_LOADER_TUNABLES">SYSCTL
-  VARIABLES AND LOADER TUNABLES</a></h1>
-<p class="Pp">The behavior of <code class="Nm">hwpmc</code> is influenced by the
-    following <a class="Xr">sysctl(8)</a> and <a class="Xr">loader(8)</a>
-    tunables:</p>
-<dl class="Bl-tag">
-  <dt id="kern.hwpmc.callchaindepth"><var class="Va">kern.hwpmc.callchaindepth</var>
-    (integer, read-only)</dt>
-  <dd>The maximum number of call chain records to capture per sample. The
-      default is 8.</dd>
-  <dt id="kern.hwpmc.debugflags"><var class="Va">kern.hwpmc.debugflags</var>
-    (string, read-write)</dt>
-  <dd>(Only available if the <code class="Nm">hwpmc</code> driver was compiled
-      with <code class="Fl">-DDEBUG</code>.) Control the verbosity of debug
-      messages from the <code class="Nm">hwpmc</code> driver.</dd>
-  <dt id="kern.hwpmc.hashsize"><var class="Va">kern.hwpmc.hashsize</var>
-    (integer, read-only)</dt>
-  <dd>The number of rows in the hash tables used to keep track of owner and
-      target processes. The default is 16.</dd>
-  <dt id="kern.hwpmc.logbuffersize"><var class="Va">kern.hwpmc.logbuffersize</var>
-    (integer, read-only)</dt>
-  <dd>The size in kilobytes of each log buffer used by
-      <code class="Nm">hwpmc</code>'s logging function. The default buffer size
-      is 256KB. The maximum value is 16MB.</dd>
-  <dt id="kern.hwpmc.mincount"><var class="Va">kern.hwpmc.mincount</var>
-    (integer, read-write)</dt>
-  <dd>The minimum sampling rate for sampling mode PMCs. The default count is
-      1000 events.</dd>
-  <dt id="kern.hwpmc.mtxpoolsize"><var class="Va">kern.hwpmc.mtxpoolsize</var>
-    (integer, read-only)</dt>
-  <dd>The size of the spin mutex pool used by the PMC driver. The default is
-    32.</dd>
-  <dt id="kern.hwpmc.nbuffers_pcpu"><var class="Va">kern.hwpmc.nbuffers_pcpu</var>
-    (integer, read-only)</dt>
-  <dd>The number of log buffers per CPU used by <code class="Nm">hwpmc</code>
-      for logging. The default is 32. The product of
-      <var class="Va">kern.hwpmc.nbuffers_pcpu</var> and
-      <var class="Va">kern.hwpmc.logbuffersize</var> must not exceed 32MB per
-      CPU.</dd>
-  <dt id="kern.hwpmc.nsamples"><var class="Va">kern.hwpmc.nsamples</var>
-    (integer, read-only)</dt>
-  <dd>The number of entries in the per-CPU ring buffer used during sampling. The
-      default is 512.</dd>
-  <dt id="security.bsd.unprivileged_syspmcs"><var class="Va">security.bsd.unprivileged_syspmcs</var>
-    (boolean, read-write)</dt>
-  <dd>If set to non-zero, allow unprivileged processes to allocate system-wide
-      PMCs. The default value is 0.</dd>
-  <dt id="security.bsd.unprivileged_proc_debug"><var class="Va">security.bsd.unprivileged_proc_debug</var>
-    (boolean, read-write)</dt>
-  <dd>If set to 0, the <code class="Nm">hwpmc</code> driver will only allow
-      privileged processes to attach PMCs to other processes.</dd>
-</dl>
-<p class="Pp">These variables may be set in the kernel environment using
-    <a class="Xr">kenv(1)</a> before <code class="Nm">hwpmc</code> is
-  loaded.</p>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="IMPLEMENTATION_NOTES"><a class="permalink" href="#IMPLEMENTATION_NOTES">IMPLEMENTATION
-  NOTES</a></h1>
-<section class="Ss">
-<h2 class="Ss" id="SMP_Symmetry"><a class="permalink" href="#SMP_Symmetry">SMP
-  Symmetry</a></h2>
-<p class="Pp">The kernel driver requires all physical CPUs in an SMP system to
-    have identical performance monitoring counter hardware.</p>
-</section>
-<section class="Ss">
-<h2 class="Ss" id="Sparse_CPU_Numbering"><a class="permalink" href="#Sparse_CPU_Numbering">Sparse
-  CPU Numbering</a></h2>
-<p class="Pp">On platforms that sparsely number CPUs and which support
-    hot-plugging of CPUs, requests that specify non-existent or disabled CPUs
-    will fail with an error. Applications allocating system-scope PMCs need to
-    be aware of the possibility of such transient failures.</p>
-</section>
-<section class="Ss">
-<h2 class="Ss" id="x86_TSC_Handling"><a class="permalink" href="#x86_TSC_Handling">x86
-  TSC Handling</a></h2>
-<p class="Pp">Historically, on the x86 architecture,
-    <span class="Ux">FreeBSD</span> has permitted user processes running at a
-    processor CPL of 3 to read the TSC using the RDTSC instruction. The
-    <code class="Nm">hwpmc</code> driver preserves this behavior.</p>
-</section>
-<section class="Ss">
-<h2 class="Ss" id="Intel_P4/HTT_Handling"><a class="permalink" href="#Intel_P4/HTT_Handling">Intel
-  P4/HTT Handling</a></h2>
-<p class="Pp">On CPUs with HTT support, Intel P4 PMCs are capable of qualifying
-    only a subset of hardware events on a per-logical CPU basis. Consequently,
-    if HTT is enabled on a system with Intel Pentium P4 PMCs, then the
-    <code class="Nm">hwpmc</code> driver will reject allocation requests for
-    process-private PMCs that request counting of hardware events that cannot be
-    counted separately for each logical CPU.</p>
-</section>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="DIAGNOSTICS"><a class="permalink" href="#DIAGNOSTICS">DIAGNOSTICS</a></h1>
-<dl class="Bl-diag">
-  <dt>hwpmc: [class/npmc/capabilities]...</dt>
-  <dd>Announce the presence of <var class="Va">npmc</var> PMCs of class
-      <var class="Va">class</var>, with capabilities described by bit string
-      <var class="Va">capabilities</var>.</dd>
-  <dt>hwpmc: kernel version (0x%x) does not match module version (0x%x).</dt>
-  <dd>The module loading process failed because a version mismatch was detected
-      between the currently executing kernel and the module being loaded.</dd>
-  <dt>hwpmc: this kernel has not been compiled with 'options HWPMC_HOOKS'.</dt>
-  <dd>The module loading process failed because the currently executing kernel
-      was not configured with the required configuration option
-      <code class="Dv">HWPMC_HOOKS</code>.</dd>
-  <dt>hwpmc: tunable hashsize=%d must be greater than zero.</dt>
-  <dd>A negative value was supplied for tunable
-      <var class="Va">kern.hwpmc.hashsize</var>.</dd>
-  <dt>hwpmc: logbuffersize=%d must be greater than zero and less than or equal
-    to %d, resetting to %d.</dt>
-  <dd>A negative value was supplied for tunable
-      <var class="Va">kern.hwpmc.logbuffersize</var>.</dd>
-  <dt>hwpmc: nbuffers_pcpu=%d must be greater than zero, resetting to %d.</dt>
-  <dd>A negative value was supplied for tunable
-      <var class="Va">kern.hwpmc.nbuffers_pcpu</var>.</dd>
-  <dt>hwpmc: tunable nsamples=%d out of range.</dt>
-  <dd>The value for tunable <var class="Va">kern.hwpmc.nsamples</var> was
-      negative or greater than 65535.</dd>
-  <dt>hwpmc: nbuffers_pcpu=%d * logbuffersize=%d exceeds %dMB per CPU limit,
-    resetting to defaults (%d * %d).</dt>
-  <dd>The product of tunables <var class="Va">kern.hwpmc.nbuffers_pcpu</var> and
-      <var class="Va">kern.hwpmc.logbuffersize</var> exceeds the maximum per-CPU
-      memory limit. Both tunables are reset to their compiled defaults.</dd>
-</dl>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="DEBUGGING"><a class="permalink" href="#DEBUGGING">DEBUGGING</a></h1>
-<p class="Pp">The <code class="Nm">hwpmc</code> module can be configured to
-    record trace entries using the <a class="Xr">ktr(4)</a> interface. This is
-    useful for debugging the driver's functionality, primarily during
-    development. This debugging functionality is not enabled by default, and
-    requires recompiling the kernel and <code class="Nm">hwpmc</code> module
-    after adding the following to the kernel config:</p>
-<div class="Bd Pp Bd-indent Li">
-<pre><code class="Cd">options KTR</code>
-<code class="Cd">options KTR_COMPILE=(KTR_SUBSYS)</code>
-<code class="Cd">options KTR_MASK=(KTR_SUBSYS)</code>
-<code class="Cd">options HWPMC_DEBUG</code></pre>
-</div>
-<p class="Pp">This alone is not enough to enable tracing; one must also
-    configure the <var class="Va">kern.hwpmc.debugflags</var>
-    <a class="Xr">sysctl(8)</a> variable, which provides fine-grained control
-    over which types of events are logged to the trace buffer.</p>
-<p class="Pp"><code class="Nm">hwpmc</code> trace events are grouped by 'major'
-    and 'minor' flag types. The major flag names are as follows:</p>
-<p class="Pp"></p>
-<div class="Bd-indent">
-<dl class="Bl-tag Bl-compact">
-  <dt>cpu</dt>
-  <dd>CPU events</dd>
-  <dt>csw</dt>
-  <dd>Context switch events</dd>
-  <dt>logging</dt>
-  <dd>Logging events</dd>
-  <dt>md</dt>
-  <dd>Machine-dependent/class-dependent events</dd>
-  <dt>module</dt>
-  <dd>Miscellaneous events</dd>
-  <dt>owner</dt>
-  <dd>PMC owner events</dd>
-  <dt>pmc</dt>
-  <dd>PMC management events</dd>
-  <dt>process</dt>
-  <dd>Process events</dd>
-  <dt>sampling</dt>
-  <dd>Sampling events</dd>
-</dl>
-</div>
-<p class="Pp">The minor flags for each major flag group can vary. The individual
-    minor flag names are:</p>
-<div class="Bd Pp Bd-indent">allocaterow, allocate, attach, bind, config, exec,
-  exit, find, flush, fork, getbuf, hook, init, intr, linktarget, mayberemove,
-  ops, read, register, release, remove, sample, scheduleio, select, signal, swi,
-  swo, start, stop, syscall, unlinktarget, write</div>
-<p class="Pp">The <var class="Va">kern.hwpmc.debugflags</var> variable is a
-    string with a custom format. The string should contain a space-separated
-    list of event specifiers. Each event specifier consists of the major flag
-    name, followed by an equal sign (=), followed by a comma-separated list of
-    minor event types. To track all events for a major group, an asterisk (*)
-    can be given instead of minor event names.</p>
-<p class="Pp">For example, to trace all allocation and release events, set
-    <var class="Va">debugflags</var> as follows:</p>
-<div class="Bd Pp Bd-indent Li">
-<pre>kern.hwpmc.debugflags=&quot;pmc=allocate,release md=allocate,release&quot;</pre>
-</div>
-<p class="Pp">To trace all events in the process and context switch major flag
-    groups:</p>
-<div class="Bd Pp Bd-indent Li">
-<pre>kern.hwpmc.debugflags=&quot;process=* csw=*&quot;</pre>
-</div>
-<p class="Pp">To disable all trace events, set the variable to an empty
-  string.</p>
-<div class="Bd Pp Bd-indent Li">
-<pre>kern.hwpmc.debugflags=&quot;&quot;</pre>
-</div>
-<p class="Pp">Trace events are recorded by <a class="Xr">ktr(4)</a>, and can be
-    inspected at run-time using the <a class="Xr">ktrdump(8)</a> utility, or at
-    the <a class="Xr">ddb(4)</a> prompt after a panic with the 'show ktr'
-    command.</p>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="ERRORS"><a class="permalink" href="#ERRORS">ERRORS</a></h1>
-<p class="Pp">A command issued to the <code class="Nm">hwpmc</code> driver may
-    fail with the following errors:</p>
-<dl class="Bl-tag">
-  <dt id="EAGAIN">[<a class="permalink" href="#EAGAIN"><code class="Er">EAGAIN</code></a>]</dt>
-  <dd>Helper process creation failed for a
-      <code class="Dv">PMC_OP_CONFIGURELOG</code> request due to a temporary
-      resource shortage in the kernel.</dd>
-  <dt id="EBUSY">[<a class="permalink" href="#EBUSY"><code class="Er">EBUSY</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_CONFIGURELOG</code> operation was requested
-      while an existing log was active.</dd>
-  <dt id="EBUSY~2">[<a class="permalink" href="#EBUSY~2"><code class="Er">EBUSY</code></a>]</dt>
-  <dd>A DISABLE operation was requested using the
-      <code class="Dv">PMC_OP_PMCADMIN</code> request for a set of hardware
-      resources currently in use for process-private PMCs.</dd>
-  <dt id="EBUSY~3">[<a class="permalink" href="#EBUSY~3"><code class="Er">EBUSY</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCADMIN</code> operation was requested on an
-      active system mode PMC.</dd>
-  <dt id="EBUSY~4">[<a class="permalink" href="#EBUSY~4"><code class="Er">EBUSY</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCATTACH</code> operation was requested for a
-      target process that already had another PMC using the same hardware
-      resources attached to it.</dd>
-  <dt id="EBUSY~5">[<a class="permalink" href="#EBUSY~5"><code class="Er">EBUSY</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCRW</code> request writing a new value was
-      issued on a PMC that was active.</dd>
-  <dt id="EBUSY~6">[<a class="permalink" href="#EBUSY~6"><code class="Er">EBUSY</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCSETCOUNT</code> request was issued on a PMC
-      that was active.</dd>
-  <dt id="EDOOFUS">[<a class="permalink" href="#EDOOFUS"><code class="Er">EDOOFUS</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCSTART</code> operation was requested without
-      a log file being configured for a PMC allocated with
-      <code class="Dv">PMC_F_LOG_PROCCSW</code> and
-      <code class="Dv">PMC_F_LOG_PROCEXIT</code> modifiers.</dd>
-  <dt id="EDOOFUS~2">[<a class="permalink" href="#EDOOFUS~2"><code class="Er">EDOOFUS</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCSTART</code> operation was requested on a
-      system-wide sampling PMC without a log file being configured.</dd>
-  <dt id="EEXIST">[<a class="permalink" href="#EEXIST"><code class="Er">EEXIST</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCATTACH</code> request was reissued for a
-      target process that already is the target of this PMC.</dd>
-  <dt id="EFAULT">[<a class="permalink" href="#EFAULT"><code class="Er">EFAULT</code></a>]</dt>
-  <dd>A bad address was passed in to the driver.</dd>
-  <dt id="EINVAL">[<a class="permalink" href="#EINVAL"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>An invalid PMC handle was specified.</dd>
-  <dt id="EINVAL~2">[<a class="permalink" href="#EINVAL~2"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>An invalid CPU number was passed in for a
-      <code class="Dv">PMC_OP_GETPMCINFO</code> operation.</dd>
-  <dt id="EINVAL~3">[<a class="permalink" href="#EINVAL~3"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>The <var class="Ar">pm_flags</var> argument to a
-      <code class="Dv">PMC_OP_CONFIGURELOG</code> request contained unknown
-      flags.</dd>
-  <dt id="EINVAL~4">[<a class="permalink" href="#EINVAL~4"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_CONFIGURELOG</code> request to de-configure a
-      log file was issued without a log file being configured.</dd>
-  <dt id="EINVAL~5">[<a class="permalink" href="#EINVAL~5"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_FLUSHLOG</code> request was issued without a log
-      file being configured.</dd>
-  <dt id="EINVAL~6">[<a class="permalink" href="#EINVAL~6"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>An invalid CPU number was passed in for a
-      <code class="Dv">PMC_OP_PMCADMIN</code> operation.</dd>
-  <dt id="EINVAL~7">[<a class="permalink" href="#EINVAL~7"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>An invalid operation request was passed in for a
-      <code class="Dv">PMC_OP_PMCADMIN</code> operation.</dd>
-  <dt id="EINVAL~8">[<a class="permalink" href="#EINVAL~8"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>An invalid PMC ID was passed in for a
-      <code class="Dv">PMC_OP_PMCADMIN</code> operation.</dd>
-  <dt id="EINVAL~9">[<a class="permalink" href="#EINVAL~9"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>A suitable PMC matching the parameters passed in to a
-      <code class="Dv">PMC_OP_PMCALLOCATE</code> request could not be
-    allocated.</dd>
-  <dt id="EINVAL~10">[<a class="permalink" href="#EINVAL~10"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>An invalid PMC mode was requested during a
-      <code class="Dv">PMC_OP_PMCALLOCATE</code> request.</dd>
-  <dt id="EINVAL~11">[<a class="permalink" href="#EINVAL~11"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>An invalid CPU number was specified during a
-      <code class="Dv">PMC_OP_PMCALLOCATE</code> request.</dd>
-  <dt id="EINVAL~12">[<a class="permalink" href="#EINVAL~12"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>A CPU other than <code class="Dv">PMC_CPU_ANY</code> was specified in a
-      <code class="Dv">PMC_OP_PMCALLOCATE</code> request for a process-private
-      PMC.</dd>
-  <dt id="EINVAL~13">[<a class="permalink" href="#EINVAL~13"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>A CPU number of <code class="Dv">PMC_CPU_ANY</code> was specified in a
-      <code class="Dv">PMC_OP_PMCALLOCATE</code> request for a system-wide
-    PMC.</dd>
-  <dt id="EINVAL~14">[<a class="permalink" href="#EINVAL~14"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>The <var class="Ar">pm_flags</var> argument to an
-      <code class="Dv">PMC_OP_PMCALLOCATE</code> request contained unknown
-      flags.</dd>
-  <dt id="EINVAL~15">[<a class="permalink" href="#EINVAL~15"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>(On Intel Pentium 4 CPUs with HTT support) A
-      <code class="Dv">PMC_OP_PMCALLOCATE</code> request for a process-private
-      PMC was issued for an event that does not support counting on a
-      per-logical CPU basis.</dd>
-  <dt id="EINVAL~16">[<a class="permalink" href="#EINVAL~16"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>A PMC allocated for system-wide operation was specified with a
-      <code class="Dv">PMC_OP_PMCATTACH</code> or
-      <code class="Dv">PMC_OP_PMCDETACH</code> request.</dd>
-  <dt id="EINVAL~17">[<a class="permalink" href="#EINVAL~17"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>The <var class="Ar">pm_pid</var> argument to a
-      <code class="Dv">PMC_OP_PMCATTACH</code> or
-      <code class="Dv">PMC_OP_PMCDETACH</code> request specified an illegal
-      process ID.</dd>
-  <dt id="EINVAL~18">[<a class="permalink" href="#EINVAL~18"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCDETACH</code> request was issued for a PMC
-      not attached to the target process.</dd>
-  <dt id="EINVAL~19">[<a class="permalink" href="#EINVAL~19"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>Argument <var class="Ar">pm_flags</var> to a
-      <code class="Dv">PMC_OP_PMCRW</code> request contained illegal flags.</dd>
-  <dt id="EINVAL~20">[<a class="permalink" href="#EINVAL~20"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCX86GETMSR</code> operation was requested for
-      a PMC not in process-virtual mode, or for a PMC that is not solely
-      attached to its owner process, or for a PMC that was allocated with flag
-      <code class="Dv">PMC_F_DESCENDANTS</code>.</dd>
-  <dt id="EINVAL~21">[<a class="permalink" href="#EINVAL~21"><code class="Er">EINVAL</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_WRITELOG</code> request was issued for an owner
-      process without a log file configured.</dd>
-  <dt id="ENOMEM">[<a class="permalink" href="#ENOMEM"><code class="Er">ENOMEM</code></a>]</dt>
-  <dd>The system was not able to allocate kernel memory.</dd>
-  <dt id="ENOSYS">[<a class="permalink" href="#ENOSYS"><code class="Er">ENOSYS</code></a>]</dt>
-  <dd>(On i386 and amd64 architectures) A
-      <code class="Dv">PMC_OP_PMCX86GETMSR</code> operation was requested for
-      hardware that does not support reading PMCs directly with the RDPMC
-      instruction.</dd>
-  <dt id="ENXIO">[<a class="permalink" href="#ENXIO"><code class="Er">ENXIO</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_GETPMCINFO</code> operation was requested for an
-      absent or disabled CPU.</dd>
-  <dt id="ENXIO~2">[<a class="permalink" href="#ENXIO~2"><code class="Er">ENXIO</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCALLOCATE</code> operation specified
-      allocation of a system-wide PMC on an absent or disabled CPU.</dd>
-  <dt id="ENXIO~3">[<a class="permalink" href="#ENXIO~3"><code class="Er">ENXIO</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCSTART</code> or
-      <code class="Dv">PMC_OP_PMCSTOP</code> request was issued for a
-      system-wide PMC that was allocated on a CPU that is currently absent or
-      disabled.</dd>
-  <dt id="EOPNOTSUPP">[<a class="permalink" href="#EOPNOTSUPP"><code class="Er">EOPNOTSUPP</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCALLOCATE</code> request was issued for PMC
-      capabilities not supported by the specified PMC class.</dd>
-  <dt id="EOPNOTSUPP~2">[<a class="permalink" href="#EOPNOTSUPP~2"><code class="Er">EOPNOTSUPP</code></a>]</dt>
-  <dd>(i386 architectures) A sampling mode PMC was requested on a CPU lacking an
-      APIC.</dd>
-  <dt id="EPERM">[<a class="permalink" href="#EPERM"><code class="Er">EPERM</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCADMIN</code> request was issued by a process
-      without super-user privilege or by a jailed super-user process.</dd>
-  <dt id="EPERM~2">[<a class="permalink" href="#EPERM~2"><code class="Er">EPERM</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCATTACH</code> operation was issued for a
-      target process that the current process does not have permission to attach
-      to.</dd>
-  <dt id="EPERM~3">[<a class="permalink" href="#EPERM~3"><code class="Er">EPERM</code></a>]</dt>
-  <dd>(i386 and amd64 architectures) A <code class="Dv">PMC_OP_PMCATTACH</code>
-      operation was issued on a PMC whose MSR has been retrieved using
-      <code class="Dv">PMC_OP_PMCX86GETMSR</code>.</dd>
-  <dt id="ESRCH">[<a class="permalink" href="#ESRCH"><code class="Er">ESRCH</code></a>]</dt>
-  <dd>A process issued a PMC operation request without having allocated any
-      PMCs.</dd>
-  <dt id="ESRCH~2">[<a class="permalink" href="#ESRCH~2"><code class="Er">ESRCH</code></a>]</dt>
-  <dd>A process issued a PMC operation request after the PMC was detached from
-      all of its target processes.</dd>
-  <dt id="ESRCH~3">[<a class="permalink" href="#ESRCH~3"><code class="Er">ESRCH</code></a>]</dt>
-  <dd>A <code class="Dv">PMC_OP_PMCATTACH</code> or
-      <code class="Dv">PMC_OP_PMCDETACH</code> request specified a non-existent
-      process ID.</dd>
-  <dt id="ESRCH~4">[<a class="permalink" href="#ESRCH~4"><code class="Er">ESRCH</code></a>]</dt>
-  <dd>The target process for a <code class="Dv">PMC_OP_PMCDETACH</code>
-      operation is not being monitored by <code class="Nm">hwpmc</code>.</dd>
-</dl>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
-  ALSO</a></h1>
-<p class="Pp"><a class="Xr">kenv(1)</a>, <a class="Xr">pmc(3)</a>,
-    <a class="Xr">pmclog(3)</a>, <a class="Xr">ddb(4)</a>,
-    <a class="Xr">ktr(4)</a>, <a class="Xr">kldload(8)</a>,
-    <a class="Xr">ktrdump(8)</a>, <a class="Xr">pmccontrol(8)</a>,
-    <a class="Xr">pmcstat(8)</a>, <a class="Xr">sysctl(8)</a>,
-    <a class="Xr">kproc_create(9)</a>, <a class="Xr">p_candebug(9)</a></p>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
-<p class="Pp">The <code class="Nm">hwpmc</code> driver first appeared in
-    <span class="Ux">FreeBSD 6.0</span>.</p>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="AUTHORS"><a class="permalink" href="#AUTHORS">AUTHORS</a></h1>
-<p class="Pp">The <code class="Nm">hwpmc</code> driver was written by
-    <span class="An">Joseph Koshy</span>
-    &lt;<a class="Mt" href="mailto:jkoshy@FreeBSD.org">jkoshy@FreeBSD.org</a>&gt;.</p>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="BUGS"><a class="permalink" href="#BUGS">BUGS</a></h1>
-<p class="Pp">The driver samples the state of the kernel's logical processor
-    support at the time of initialization (i.e., at module load time). On CPUs
-    supporting logical processors, the driver could misbehave if logical
-    processors are subsequently enabled or disabled while the driver is
-  active.</p>
-<p class="Pp">On the i386 architecture, the driver requires that the local APIC
-    on the CPU be enabled for sampling mode to be supported. Many
-    single-processor motherboards keep the APIC disabled in BIOS; on such
-    systems <code class="Nm">hwpmc</code> will not support sampling PMCs.</p>
-</section>
-<section class="Sh">
-<h1 class="Sh" id="SECURITY_CONSIDERATIONS"><a class="permalink" href="#SECURITY_CONSIDERATIONS">SECURITY
-  CONSIDERATIONS</a></h1>
-<p class="Pp">PMCs may be used to monitor the actual behavior of the system on
-    hardware. In situations where this constitutes an undesirable information
-    leak, the following options are available:</p>
-<ol class="Bl-enum">
-  <li>Set the <a class="Xr">sysctl(8)</a> tunable
-      <var class="Va">security.bsd.unprivileged_syspmcs</var> to 0. This ensures
-      that unprivileged processes cannot allocate system-wide PMCs and thus
-      cannot observe the hardware behavior of the system as a whole. This
-      tunable may also be set at boot time using <a class="Xr">loader(8)</a>, or
-      with <a class="Xr">kenv(1)</a> prior to loading the
-      <code class="Nm">hwpmc</code> driver into the kernel.</li>
-  <li>Set the <a class="Xr">sysctl(8)</a> tunable
-      <var class="Va">security.bsd.unprivileged_proc_debug</var> to 0. This will
-      ensure that an unprivileged process cannot attach a PMC to any process
-      other than itself and thus cannot observe the hardware behavior of other
-      processes with the same credentials.</li>
-</ol>
-<p class="Pp">System administrators should note that on IA-32 platforms
-    <span class="Ux">FreeBSD</span> makes the content of the IA-32 TSC counter
-    available to all processes via the RDTSC instruction.</p>
-</section>
-</div>
-<table class="foot">
-  <tr>
-    <td class="foot-date">July 8, 2023</td>
-    <td class="foot-os">FreeBSD 15.0</td>
-  </tr>
-</table>