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SubjectRe: [patch 3/3] From: Ben Segall <>
[snip]

> Since throttling occurs in the put_prev_task() path we do not get to observe
> this delta against nr_running when making the decision to idle_balance().
>
> Fix this by first enumerating cfs_rq throttle states so that we can distinguish
> throttling cfs_rqs. Then remove tasks that will be throttled in put_prev_task
> from rq->nr_running/cfs_rq->h_nr_running when in account_cfs_rq_runtime,
> rather than delaying until put_prev_task.
>
> This allows schedule() to call idle_balance when we go idle due to throttling.
>
> Using Kamalesh's nested-cgroup test case[1] we see the following improvement on
> a 16 core system:
> baseline: Average CPU Idle percentage 13.9667%
> +patch: Average CPU Idle percentage 3.53333%
> [1]: https://lkml.org/lkml/2011/9/15/261
>
> Signed-off-by: Ben Segall <bsegall@google.com>
> Signed-off-by: Paul Turner <pjt@google.com>

Tested-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>

Thanks for the patch. I tested patches on the same test environment, over which
the cpu idle time was reported first at https://lkml.org/lkml/2011/6/7/352. In
brief, tests were run on 2 socket quad core machine with three level of nested
cgroups hierarchy and five cgroups created below the third level. Each of the
five cgroups, having 2,2,4,8,16 while1 or cpu-matrix (https://lkml.org/lkml/2011/11/4/107)
tasks attached to them respectively.

[1] CFS Bandwith tweaks, were the patches posted by Paul Turner (https://lkml.org/lkml/2011/11/7/603)
[2] nohz idle balance RFC patch by Srivatsa Vaddagiri (https://lkml.org/lkml/2011/11/2/117)

While running the cpu-matrix benchmark with the patches, there was an improvement
around ~50 to 55% and additional ~3% benefit in idle time with nohz idle balance
patch. With while1 loop the improvment was around ~36 to 40% over tip and an
additional benefit of ~4 to 5% was seen with nohz idle balance patch.

(1) cpu-matrix benchmark with nohz=on
----------------------------------
Run Base (tip) tip + CFS Bandwith tweaks tip + CFS Bandwith tweaks + nohz idle patch
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1 Average CPU Idle percentage 4.1% Average CPU Idle percentage 2.36667% Average CPU Idle percentage 2.23333%
Bandwidth shared with remaining non-Idle 95.9% Bandwidth shared with remaining non-Idle 97.63333% Bandwidth shared with remaining non-Idle 97.76667%
2 Average CPU Idle percentage 4.23% Average CPU Idle percentage 2.3% Average CPU Idle percentage 2.16667%
Bandwidth shared with remaining non-Idle 95.77% Bandwidth shared with remaining non-Idle 97.7% Bandwidth shared with remaining non-Idle 97.83333%
(2) cpu-matrix benchmark with nohz=off
-----------------------------------
Run Base (tip) tip + CFS Bandwith tweaks tip + CFS Bandwith tweaks + nohz idle patch
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1 Average CPU Idle percentage 4.53333% Average CPU Idle percentage 2.43333% Average CPU Idle percentage 2.36667%
Bandwidth shared with remaining non-Idle 95.46667% Bandwidth shared with remaining non-Idle 97.56667% Bandwidth shared with remaining non-Idle 97.63333%
2 Average CPU Idle percentage 4.4% Average CPU Idle percentage 2.36667% Average CPU Idle percentage 2.4%
Bandwidth shared with remaining non-Idle 95.6% Bandwidth shared with remaining non-Idle 97.63333% Bandwidth shared with remaining non-Idle 97.6%

(3) while1 loop with nohz=on
-------------------------
Run Base (tip) tip + CFS Bandwith tweaks tip + CFS Bandwith tweaks + nohz idle patch
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1 Average CPU Idle percentage 6.26667% Average CPU Idle percentage 2.5% Average CPU Idle percentage 2.23333%
Bandwidth shared with remaining non-Idle 93.73333% Bandwidth shared with remaining non-Idle 97.5% Bandwidth shared with remaining non-Idle 97.76667%
2 Average CPU Idle percentage 6.73333% Average CPU Idle percentage 2.46667% Average CPU Idle percentage 2.13333%
Bandwidth shared with remaining non-Idle 93.26667% Bandwidth shared with remaining non-Idle 97.53333% Bandwidth shared with remaining non-Idle 97.86667%
(4) while1 loop with nohz=off
--------------------------
Run Base (tip) tip + CFS Bandwith tweaks tip + CFS Bandwith tweaks + nohz idle patch
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1 Average CPU Idle percentage 3.6% Average CPU Idle percentage 2.4% Average CPU Idle percentage 2.43333%
Bandwidth shared with remaining non-Idle 96.4% Bandwidth shared with remaining non-Idle 97.6% Bandwidth shared with remaining non-Idle 97.56667%
2 Average CPU Idle percentage 3.46667% Average CPU Idle percentage 2.33333% Average CPU Idle percentage 2.4%
Bandwidth shared with remaining non-Idle 96.53333% Bandwidth shared with remaining non-Idle 97.66667% Bandwidth shared with remaining non-Idle 97.6%
each cpu-matrix benchmark task was run as # perf sched cpu-matrix -s1k -i 1000 -p100

Kamalesh.



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