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diff --git a/static/v10/man5/share.5 b/static/v10/man5/share.5 new file mode 100644 index 00000000..8b70bcd8 --- /dev/null +++ b/static/v10/man5/share.5 @@ -0,0 +1,309 @@ +.TH SHARE 5 SHARE +.SH NAME +Share \- Share Scheduling on Unix +.SH SYNOPSIS +Scheduling for a share of the machine +.SH DESCRIPTION +.I Share +is a term covering those elements of the Unix kernel +that affect the priority of a user's job. +The basic scheduler in Unix schedules processes on a short term +.I per-process +basis. +The +.I "share scheduler" +takes account of the history of a user's +usage of the resources of the machine, and introduces a +.I per-user +long term scheduler. +To do this, several variables are available to the scheduler in a per-user data +structure known as an +.I lnode. +These record the intended share of the machine that the user should get, +the recent history of resources consumed (``usage''), +and the number of active (running) processes belonging to the user. +Together, these affect the priority of each of the processes +so that consumption of resources is adjusted toward the intended share. +.P +A user's +.I usage +is calculated by accumulating the charges incurred by use of resources, +and decaying the result over time. +The share scheduler affects the low-level scheduling of a user's processes +by adding the user's +.I usage +divided by the allocated share, +and multiplied by the active process count, +to the priority of a process +every time that process incurs a clock tick. +Since the larger its priority, +the less often a process is scheduled, +processes belonging to users with high +.IR usage , +low share, or many active processes +will get a smaller share of resources. +Note that at any one time, a user can use all of the resources available +provided there is no competition from others. +.SS "SCHEDULING GROUPS" +.I lnodes +are organised into a tree. +For any particular sub-tree, +the sub-tree's share of resources +is divided up between the +lnodes +according to their relative shares. +Sub-trees are also known as groups. +The root +.I lnode +of the group is the group owner, +and the leaf +.I lnodes +are its users. +The total shares issued to the group include both those issued to the owner, +as well as those issued to the users. +Both owner and users are known as group members. +The share of the group's resources +allocated to any particular member of the group +is in the proportion +of the member's shares divided by the group's shares. +.P +The most interesting group is the one at the top of the tree, +whose owner is ``root'', +and its group members are the primary scheduling groups. +\&``root'' +gets 100% of the available resources, +which is split as above between the primary scheduling groups. +.P +Not all group owners represent real users, +and in these cases there is no need to allocate them a share of resources. +Such lnodes are indicated by the \s-1NOTSHARED\s0 flag, +which causes the scheduler to ignore their shares when allocating +their group's resources among its members. +However, +the long term +.I charge +of a group owner +always includes all the charges levied on any member of its group. +.P +For reasons of system management, +\&``root'' is always allocated 100% of the resources whenever it needs them. +However, since all real users run on their own lnodes, +the \s-1NOTSHARED\s0 flag is turned on for ``root'', +and thus the primary scheduling groups +have 100% of the available resources to share between themselves. +However, for instrumentation purposes, +``root''s +.I charge +only represents its own consumption of resources, +but the total consumption of resources is accumulated in the +.I kl_temp +field of +\&``root''s +.I kern_lnode +(see +.IR lnode (5) +for details of a +.IR kern_lnode .) +.SS CHARGES +Charges making up the accumulating usage figure +are levied by default as follows:- +.RS +.PD 0 +.TP "\w'system servicesXX'u" +cpu +100% +.TP +disk i/o +0% +.TP +terminal i/o +0% +.TP +system services +0% +.TP +memory +0% +.PD +.RE +.P +Memory charges are levied every scheduler cycle, +but note that +.I root +is never charged for the memory it uses. +These charges can be varied at different times of the day to reflect +their popularity by using the command +.IR charge (1). +.P +Usage is decayed at an exponential rate intended to ensure that +all users of the machine get an equal chance to compete for resources +over a particular time period. +The default decay results in a +.I half-life +of 2 minutes. +Use +.IR charges (1) +to find out the current decay rate and resource charges. +.SS NICE +The +.IR nice (2) +system call has a slightly different effect under Share. +The +.I nice +parameter for a process now affects the rate at which its priority decays +to a higher priority over time. +.I Nicing +a process will make it run slower, +by reducing its effective share of the resources, +but it may not run slower than another user's processes +if that user has an even lower effective share of the resources. +However, processes with a +.I nice +priority of 19 are guaranteed only to run when no other processes need the CPU. +.I Niced +processes are charged less for CPU time than normal processes, +priority 19 processes are charged almost nothing for CPU time. +.SS MANAGEMENT +There are three flags that control the operation of the share scheduler. +.TP "\w'LIMSHAREXX'u" +.SM NOSHARE +This turns off the scheduler. +Since this will leave the parameters in a ``frozen'' state, +it should probably only be done at system boot time. +This flag is on by default when the system is booted, +so the command +.IR charge (1) +must be run to activate the scheduler. +Note that the program +.IR login (8) +won't attach users to their own +.I lnodes +while this flag is on, +instead each user will remain attached to +.IR root 's +lnode. +[Value 01] +.TP +.SM ADJGROUPS +This flags turns on global group effective share adjustment. +If any group is found to be getting less than +.SM MINGSHARE +times its allocated share, +then the costs incurred by its members are reduced proportionately. +[Value 02] +.TP +.SM LIMSHARE +This flag deals with an +``edge effect'' +that occurs when users first log in. +It may be that their +.I usage +field has decayed to the point where they might temporarily be allocated +nearly 100% of the machine. +This flag limits any one user's share of the resources to no more than +MAXUSHARE times their intended share. +Of course, this still may be nearly 100%, if no other users are logged in, +or the other users have very small shares. +[Value 04] +.P +The +.IR charge (1) +command is used to manipulate these flags, and the charging parameters above. +There are also other parameters which may be changed with +.IR charge :- +.TP "\w'MAXNORMUSAGEXX'u" +.BI DecayRate +The decay rate for users' +.IR "active process rates" . +This parameter is calculated by counting the active proceses +per user every clock scan, +and is decayed every clock scan. +The usual value for this should result in a +.I half-life +for the rate of about 10 seconds. +.TP +.BI DecayUsage +The decay rate for users' usages. +This may be altered to produce a +.I half-life +for usage ranging from a few seconds to many days. +.TP +.BI Delta +The run frequency of the share scheduler in seconds. +The default value of 4 is fine. +.TP +.BI MAXGROUPS +This sets the maximum group nesting (depth of scheduling tree) allowed, +not including ``root''s group. +.TP +.BI MAXPRI +Absolute upper bound for a process's priority. +.TP +.BI MAXUPRI +Upper bound for normal processes' priorities. +.I Idle +processes run with priorities in the range +\s-1MAXUPRI\s0 < \fIpri\fP < \s-1MAXPRI\s0. +.TP +.BI MAXUSAGE +Upper bound for ``reasonable'' usages. +Users with usages larger than this are grouped together and given +process priorities +which prevent them from interfering with ``normal'' users. +The usage +(multiplied by the +.IR "active process rate" ) +is added to a running process's priority +every time it incurs a clock tick, +so the upper bound should be small enough not to overrun the value +.SM MAXUPRI +in too short a time interval +.TP +.BI MAXUSERS +Sets the maximum number of users and groups that can be active. +Note that this cannot exceed the maximum configured in the kernel. +.TP +.BI PriDecay +This is the decay rate for maximally niced processes. +A reasonable minimum value for the +.I half-life +is about 100 seconds, +but see the comment for +.SM MAXUSAGE +above. +.TP +.BI PriDecayBase +The base for calculating the decay rate +for process priorities with normal \fInice\fP. +This should be set low enough so that the priorities of processes +for users with low share don't decay too quickly. +A reasonable minimum value for the +.I half-life +is about 2 seconds. +.SH FILES +.PD 0 +.TP "\w'/usr/include/sys/charges.hXX'u" +.IR /usr/include/sys/share.h +Definition of scheduler parameters. +.TP +.IR /usr/include/sys/charges.h +Default scheduler parameters. +.PD +.SH "SEE ALSO" +charge(1), +pl(1), +rates(1), +shstats(1), +ustats(1), +lnode(5), +shares(5), +login(8), +sharer(8). +.SH REFERENCES +"Scheduling for a Share of the Machine", J Larmouth, SP&E, Vol 5 1975 pp 29-49 +.br +"Scheduling for Immediate Turnaround", J Larmouth, SP&E, Vol 8 1978 pp 559-578 +.br +"A Fair Share Scheduler", J Kay & P Lauder, TM 11275-870319-01 +.br +"Share Scheduler Administration", P Lauder |