[patch 00/17] CFS Bandwidth Control v7.1
From: Paul Turner
Date: Thu Jul 07 2011 - 01:35:23 EST
Hi all,
Please find attached an incremental revision on v7 of bandwidth control.
The only real functional change is an improvement to update shares only as we
leave a throttled state. The remainder is largely refactoring, expansion of
comments, and code clean-up.
Hidetoshi Seto and Hu Tao have been kind enough to run performance benchmarks
against v7 measuring the scheduling path overheads versus pipe-test-100k.
Results can be found at:
https://lkml.org/lkml/2011/6/24/10
https://lkml.org/lkml/2011/7/4/347
The summary results (from Hu Tao's most recent run) are:
cycles instructions branches
-------------------------------------------------------------------------------------------------------------------
base 7,526,317,497 8,666,579,347 1,771,078,445
+patch, cgroup not enabled 7,610,354,447 (1.12%) 8,569,448,982 (-1.12%) 1,751,675,193 (-0.11%)
+patch, 10000000000/1000(quota/period) 7,856,873,327 (4.39%) 8,822,227,540 (1.80%) 1,801,766,182 (1.73%)
+patch, 10000000000/10000(quota/period) 7,797,711,600 (3.61%) 8,754,747,746 (1.02%) 1,788,316,969 (0.97%)
+patch, 10000000000/100000(quota/period) 7,777,784,384 (3.34%) 8,744,979,688 (0.90%) 1,786,319,566 (0.86%)
+patch, 10000000000/1000000(quota/period) 7,802,382,802 (3.67%) 8,755,638,235 (1.03%) 1,788,601,070 (0.99%)
------------------------------------------------------------------------------------------------------------------
Thanks again for running these benchmarks!
Changes:
v7.1
-----------
- We now only explicitly update entity shares as their hierarchy leaves a
throttled state. This simplifies shares interactions as all tg->shares
logic can now be omitted within a throttled hierarchy. This should also
improve the quality of balance observed within Kamalesh's nested cgroup test
as we are able to do a bottom-up shares update on unthrottle.
- do_sched_cfs_period_timer() refactored to be linear/readable.
- We now force a period timer restart in tg_set_cfs_bandwidth (before a
dramatic decrease in the period length could have induced a period of
starvation while we waited for the previous timer to expire). Also avoid a
spurious start/restart that existed in the quota == RUNTIME_INF case.
- The above removes the case of bandwidth changing within the period timer
which helps with the do_sched_cfs_period_timer() clean-up.
- Fixed potential cfs_b lock nesting on __start_cfs_bandwidth() (In the case
that we are racing with call-back startup and not tear-down).
- The load-balancer checks to ensure that we are not moving tasks between
throttled hierarchies have been refactored and now check both the src and
dest cfs_rqs.
- Buddy isolation cleaned up and moved to its own patch.
- Enabling of throttling deferred later within the series so that
load-balancer and buddy protections exist (for stability in bisection).
- Documentation given a once-over for clarity and content.
- General code cleanup & comments improved
Hidetoshi, the following patchsets have changed enough to necessitate tweaking
of your Reviewed-by:
[patch 09/18] sched: add support for unthrottling group entities (extensive)
[patch 11/18] sched: prevent interactions with throttled entities (update_cfs_shares)
[patch 12/18] sched: prevent buddy interactions with throttled entities (new)
Previous postings:
-----------------
v7: http://lkml.org/lkml/2011/6/21/43
v6: http://lkml.org/lkml/2011/5/7/37
v5: http://lkml.org/lkml/2011/3 /22/477
v4: http://lkml.org/lkml/2011/2/23/44
v3: http://lkml.org/lkml/2010/10/12/44
v2: http://lkml.org/lkml/2010/4/28/88
Original posting: http://lkml.org/lkml/2010/2/12/393
Prior approaches: http://lkml.org/lkml/2010/1/5/44 ["CFS Hard limits v5"]
Thanks,
- Paul
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