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diff --git a/static/freebsd/man4/polling.4 3.html b/static/freebsd/man4/polling.4 3.html deleted file mode 100644 index 1dc51bd1..00000000 --- a/static/freebsd/man4/polling.4 3.html +++ /dev/null @@ -1,184 +0,0 @@ -<table class="head"> - <tr> - <td class="head-ltitle">POLLING(4)</td> - <td class="head-vol">Device Drivers Manual</td> - <td class="head-rtitle">POLLING(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">polling</code> — <span class="Nd">device - polling support</span></p> -</section> -<section class="Sh"> -<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1> -<p class="Pp"><code class="Cd">options DEVICE_POLLING</code></p> -</section> -<section class="Sh"> -<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1> -<p class="Pp">Device polling ( <code class="Nm">polling</code> for brevity) - refers to a technique that lets the operating system periodically poll - devices, instead of relying on the devices to generate interrupts when they - need attention. This might seem inefficient and counterintuitive, but when - done properly, <code class="Nm">polling</code> gives more control to the - operating system on when and how to handle devices, with a number of - advantages in terms of system responsiveness and performance.</p> -<p class="Pp">In particular, <code class="Nm">polling</code> reduces the - overhead for context switches which is incurred when servicing interrupts, - and gives more control on the scheduling of the CPU between various tasks - (user processes, software interrupts, device handling) which ultimately - reduces the chances of livelock in the system.</p> -<section class="Ss"> -<h2 class="Ss" id="Principles_of_Operation"><a class="permalink" href="#Principles_of_Operation">Principles - of Operation</a></h2> -<p class="Pp">In the normal, interrupt-based mode, devices generate an interrupt - whenever they need attention. This in turn causes a context switch and the - execution of an interrupt handler which performs whatever processing is - needed by the device. The duration of the interrupt handler is potentially - unbounded unless the device driver has been programmed with real-time - concerns in mind (which is generally not the case for - <span class="Ux">FreeBSD</span> drivers). Furthermore, under heavy traffic - load, the system might be persistently processing interrupts without being - able to complete other work, either in the kernel or in userland.</p> -<p class="Pp">Device polling disables interrupts by polling devices at - appropriate times, i.e., on clock interrupts and within the idle loop. This - way, the context switch overhead is removed. Furthermore, the operating - system can control accurately how much work to spend in handling device - events, and thus prevent livelock by reserving some amount of CPU to other - tasks.</p> -<p class="Pp">Enabling <code class="Nm">polling</code> also changes the way - software network interrupts are scheduled, so there is never the risk of - livelock because packets are not processed to completion.</p> -</section> -<section class="Ss"> -<h2 class="Ss" id="Enabling_polling"><a class="permalink" href="#Enabling_polling">Enabling - polling</a></h2> -<p class="Pp">Currently only network interface drivers support the - <code class="Nm">polling</code> feature. It is turned on and off with help - of <a class="Xr">ifconfig(8)</a> command.</p> -<p class="Pp">The historic <var class="Va">kern.polling.enable</var>, which - enabled polling for all interfaces, can be replaced with the following - code:</p> -<div class="Bd Pp Li"> -<pre>for i in `ifconfig -l` ; - do ifconfig $i polling; # use -polling to disable -done</pre> -</div> -</section> -<section class="Ss"> -<h2 class="Ss" id="MIB_Variables"><a class="permalink" href="#MIB_Variables">MIB - Variables</a></h2> -<p class="Pp">The operation of <code class="Nm">polling</code> is controlled by - the following <a class="Xr">sysctl(8)</a> MIB variables:</p> -<p class="Pp"></p> -<dl class="Bl-tag Bl-compact"> - <dt id="kern.polling.user_frac"><var class="Va">kern.polling.user_frac</var></dt> - <dd>When <code class="Nm">polling</code> is enabled, and provided that there - is some work to do, up to this percent of the CPU cycles is reserved to - userland tasks, the remaining fraction being available for - <code class="Nm">polling</code> processing. Default is 50. - <p class="Pp"></p> - </dd> - <dt id="kern.polling.burst"><var class="Va">kern.polling.burst</var></dt> - <dd>Maximum number of packets grabbed from each network interface in each - timer tick. This number is dynamically adjusted by the kernel, according - to the programmed <var class="Va">user_frac</var>, - <var class="Va">burst_max</var>, CPU speed, and system load. - <p class="Pp"></p> - </dd> - <dt id="kern.polling.each_burst"><var class="Va">kern.polling.each_burst</var></dt> - <dd>The burst above is split into smaller chunks of this number of packets, - going round-robin among all interfaces registered for - <code class="Nm">polling</code>. This prevents the case that a large burst - from a single interface can saturate the IP interrupt queue - (<var class="Va">net.inet.ip.intr_queue_maxlen</var>). Default is 5. - <p class="Pp"></p> - </dd> - <dt id="kern.polling.burst_max"><var class="Va">kern.polling.burst_max</var></dt> - <dd>Upper bound for <var class="Va">kern.polling.burst</var>. Note that when - <code class="Nm">polling</code> is enabled, each interface can receive at - most (<var class="Va">HZ</var> <span class="No">*</span> - <var class="Va">burst_max</var>) packets per second unless there are spare - CPU cycles available for <code class="Nm">polling</code> in the idle loop. - This number should be tuned to match the expected load (which can be quite - high with GigE cards). Default is 150 which is adequate for 100Mbit - network and HZ=1000. - <p class="Pp"></p> - </dd> - <dt id="kern.polling.idle_poll"><var class="Va">kern.polling.idle_poll</var></dt> - <dd>Controls if <code class="Nm">polling</code> is enabled in the idle loop. - There are no reasons (other than power saving or bugs in the scheduler's - handling of idle priority kernel threads) to disable this. - <p class="Pp"></p> - </dd> - <dt id="kern.polling.reg_frac"><var class="Va">kern.polling.reg_frac</var></dt> - <dd>Controls how often (every <var class="Va">reg_frac</var> - <span class="No">/</span> <var class="Va">HZ</var> seconds) the status - registers of the device are checked for error conditions and the like. - Increasing this value reduces the load on the bus, but also delays the - error detection. Default is 20. - <p class="Pp"></p> - </dd> - <dt id="kern.polling.handlers"><var class="Va">kern.polling.handlers</var></dt> - <dd>How many active devices have registered for - <code class="Nm">polling</code>. - <p class="Pp"></p> - </dd> - <dt id="kern.polling.short_ticks"><var class="Va">kern.polling.short_ticks</var></dt> - <dd style="width: auto;"> </dd> - <dt id="kern.polling.lost_polls"><var class="Va">kern.polling.lost_polls</var></dt> - <dd style="width: auto;"> </dd> - <dt id="kern.polling.pending_polls"><var class="Va">kern.polling.pending_polls</var></dt> - <dd style="width: auto;"> </dd> - <dt id="kern.polling.residual_burst"><var class="Va">kern.polling.residual_burst</var></dt> - <dd style="width: auto;"> </dd> - <dt id="kern.polling.phase"><var class="Va">kern.polling.phase</var></dt> - <dd style="width: auto;"> </dd> - <dt id="kern.polling.suspect"><var class="Va">kern.polling.suspect</var></dt> - <dd style="width: auto;"> </dd> - <dt id="kern.polling.stalled"><var class="Va">kern.polling.stalled</var></dt> - <dd>Debugging variables.</dd> -</dl> -</section> -</section> -<section class="Sh"> -<h1 class="Sh" id="SUPPORTED_DEVICES"><a class="permalink" href="#SUPPORTED_DEVICES">SUPPORTED - DEVICES</a></h1> -<p class="Pp">Device polling requires explicit modifications to the device - drivers. As of this writing, the <a class="Xr">bge(4)</a>, - <a class="Xr">dc(4)</a>, <a class="Xr">em(4)</a>, <a class="Xr">fwe(4)</a>, - <a class="Xr">fwip(4)</a>, <a class="Xr">fxp(4)</a>, - <a class="Xr">igb(4)</a>, <a class="Xr">nfe(4)</a>, - <a class="Xr">nge(4)</a>, <a class="Xr">re(4)</a>, <a class="Xr">rl(4)</a>, - <a class="Xr">sis(4)</a>, <a class="Xr">ste(4)</a>, - <a class="Xr">stge(4)</a>, <a class="Xr">vge(4)</a>, - <a class="Xr">vr(4)</a>, and <a class="Xr">xl(4)</a> devices are supported, - with others in the works. The modifications are rather straightforward, - consisting in the extraction of the inner part of the interrupt service - routine and writing a callback function, - <a class="permalink" href="#*_poll"><code class="Fn" id="*_poll">*_poll</code></a>(), - which is invoked to probe the device for events and process them. (See the - conditionally compiled sections of the devices mentioned above for more - details.)</p> -<p class="Pp">As in the worst case the devices are only polled on clock - interrupts, in order to reduce the latency in processing packets, it is not - advisable to decrease the frequency of the clock below 1000 Hz.</p> -</section> -<section class="Sh"> -<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1> -<p class="Pp">Device polling first appeared in <span class="Ux">FreeBSD - 4.6</span> and <span class="Ux">FreeBSD 5.0</span>.</p> -</section> -<section class="Sh"> -<h1 class="Sh" id="AUTHORS"><a class="permalink" href="#AUTHORS">AUTHORS</a></h1> -<p class="Pp">Device polling was written by <span class="An">Luigi Rizzo</span> - <<a class="Mt" href="mailto:luigi@iet.unipi.it">luigi@iet.unipi.it</a>>.</p> -</section> -</div> -<table class="foot"> - <tr> - <td class="foot-date">December 26, 2020</td> - <td class="foot-os">FreeBSD 15.0</td> - </tr> -</table> |