|| ||Preeti U Murthy <email@example.com> |
|| ||firstname.lastname@example.org |
|| ||[RFC PATCH 0/2] sched: Load Balancing using Per-entity-Load-tracking |
|| ||Fri, 12 Oct 2012 10:20:36 +0530|
|| ||email@example.com, firstname.lastname@example.org, email@example.com|
|| ||Article, Thread
This patchset uses the per-entity-load-tracking patchset which will soon be
available in the kernel.It is based on the tip/master tree and the first 8
latest patches of sched:per-entity-load-tracking alone have been imported to
the tree to avoid the complexities of task groups and to hold back the
optimizations of this patch for now.
This patchset is an attempt to begin the integration of Per-entity-load-
metric for the cfs_rq,henceforth referred to as PJT's metric,with the load
balancer in a step wise fashion,and progress based on the consequences.
The following issues have been considered towards this:
[NOTE:an x% task referred to in the logs and below is calculated over a
duty cycle of 10ms.]
1.Consider a scenario,where there are two 10% tasks running on a cpu.The
present code will consider the load on this queue to be 2048,while
using PJT's metric the load is calculated to be <1000,rarely exceeding this
limit.Although the tasks are not contributing much to the cpu load,they are
decided to be moved by the scheduler.
But one could argue that 'not moving one of these tasks could throttle
them.If there was an idle cpu,perhaps we could have moved them'.While the
power save mode would have been fine with not moving the task,the
performance mode would prefer not to throttle the tasks.We could strive
to strike a balance by making this decision tunable with certain parameters.
This patchset includes such tunables.This issue is addressed in Patch[1/2].
2.We need to be able to do this cautiously,as the scheduler code is too
complex.This patchset is an attempt to begin the integration of PJT's
metric with the load balancer in a step wise fashion,and progress based on
I dont intend to vary the parameters used by the load balancer.Some
parameters are however included anew to make decisions about including a
sched group as a candidate for load balancing.
This patchset therefore has two primary aims.
Patch[1/2]: This patch aims at detecting short running tasks and
prevent their movement.In update_sg_lb_stats,dismiss a sched group
as a candidate for load balancing,if load calculated by PJT's metric
says that the average load on the sched_group <= 1024+(.15*1024).
This is a tunable,which can be varied after sufficient experiments.
Patch[2/2]:In the current scheduler greater load would be analogous
to more number of tasks.Therefore when the busiest group is picked
from the sched domain in update_sd_lb_stats,only the loads of the
groups are compared between them.If we were to use PJT's metric,a
higher load does not necessarily mean more number of tasks.This
patch addresses this issue.
3.The next step towards integration should be in using the PJT's metric for
comparison between the loads of the busy sched group and the sched
group which has to pull the tasks,which happens in find_busiest_group.
Preeti U Murthy (2):
sched:Prevent movement of short running tasks during load balancing
sched:Pick the apt busy sched group during load balancing
kernel/sched/fair.c | 38 +++++++++++++++++++++++++++++++++++---
1 file changed, 35 insertions(+), 3 deletions(-)
Preeti U Murthy
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