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Date: Mon, 9 Nov 2009 14:43:10 +0530 From: Bharata B Rao <bharata@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org Cc: Dhaval Giani <dhaval@...ux.vnet.ibm.com>, Balbir Singh <balbir@...ux.vnet.ibm.com>, Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>, Gautham R Shenoy <ego@...ibm.com>, Srivatsa Vaddagiri <vatsa@...ibm.com>, Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>, Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Pavel Emelyanov <xemul@...nvz.org>, Herbert Poetzl <herbert@...hfloor.at>, Avi Kivity <avi@...hat.com>, Chris Friesen <cfriesen@...tel.com>, Paul Menage <menage@...gle.com>, Mike Waychison <mikew@...gle.com> Subject: [RFC v3 PATCH 7/7] sched: Hard limits documentation sched: Hard limits documentation From: Bharata B Rao <bharata@...ux.vnet.ibm.com> Documentation for hard limits feature. Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com> --- Documentation/scheduler/sched-cfs-hard-limits.txt | 48 +++++++++++++++++++++ 1 files changed, 48 insertions(+), 0 deletions(-) create mode 100644 Documentation/scheduler/sched-cfs-hard-limits.txt diff --git a/Documentation/scheduler/sched-cfs-hard-limits.txt b/Documentation/scheduler/sched-cfs-hard-limits.txt new file mode 100644 index 0000000..d6387af --- /dev/null +++ b/Documentation/scheduler/sched-cfs-hard-limits.txt @@ -0,0 +1,48 @@ +CPU HARD LIMITS FOR CFS GROUPS +============================== + +1. Overview +2. Interface +3. Examples + +1. Overview +----------- + +CFS is a proportional share scheduler which tries to divide the CPU time +proportionately between tasks or groups of tasks (task group/cgroup) depending +on the priority/weight of the task or shares assigned to groups of tasks. +In CFS, a task/task group can get more than its share of CPU if there are +enough idle CPU cycles available in the system, due to the work conserving +nature of the scheduler. However in certain scenarios (like pay-per-use), +it is desirable not to provide extra time to a group even in the presence +of idle CPU cycles. This is where hard limiting can be of use. + +Hard limits for task groups can be set by specifying how much CPU runtime a +group can consume within a given period. If the group consumes more CPU time +than the runtime in a given period, it gets throttled. None of the tasks of +the throttled group gets to run until the runtime of the group gets refreshed +at the beginning of the next period. + +2. Interface +------------ + +Hard limit feature adds 2 cgroup files for CFS group scheduler: + +cfs_runtime_us: Hard limit for the group in microseconds. + +cfs_period_us: Time period in microseconds within which hard limits is +enforced. + +A group gets created with default values for runtime (infinite runtime which +means hard limits disabled) and period (0.5s). Each group can set its own +values for runtime and period independent of other groups in the system. + +3. Examples +----------- + +# mount -t cgroup -ocpu none /cgroups/ +# cd /cgroups +# mkdir 1 +# cd 1/ +# echo 250000 > cfs_runtime_us /* set a 250ms runtime or limit */ +# echo 500000 > cfs_period_us /* set a 500ms period */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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