Messages in this thread | | | Date | Fri, 19 Jun 2020 15:51:23 +0100 | From | Qais Yousef <> | Subject | Re: [PATCH 2/2] sched/uclamp: Protect uclamp fast path code with static key |
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On 06/19/20 12:57, Mel Gorman wrote: > On Fri, Jun 19, 2020 at 11:36:46AM +0100, Valentin Schneider wrote: > > > nouclamp uclamp uclamp-static-key > > > Hmean send-64 162.43 ( 0.00%) 157.84 * -2.82%* 163.39 * 0.59%* > > > Hmean send-128 324.71 ( 0.00%) 314.78 * -3.06%* 326.18 * 0.45%* > > > Hmean send-256 641.55 ( 0.00%) 628.67 * -2.01%* 648.12 * 1.02%* > > > Hmean send-1024 2525.28 ( 0.00%) 2448.26 * -3.05%* 2543.73 * 0.73%* > > > Hmean send-2048 4836.14 ( 0.00%) 4712.08 * -2.57%* 4867.69 * 0.65%* > > > Hmean send-3312 7540.83 ( 0.00%) 7425.45 * -1.53%* 7621.06 * 1.06%* > > > Hmean send-4096 9124.53 ( 0.00%) 8948.82 * -1.93%* 9276.25 * 1.66%* > > > Hmean send-8192 15589.67 ( 0.00%) 15486.35 * -0.66%* 15819.98 * 1.48%* > > > Hmean send-16384 26386.47 ( 0.00%) 25752.25 * -2.40%* 26773.74 * 1.47%* > > > > > > > Am I reading this correctly in that compiling in uclamp but having the > > static key enabled gives a slight improvement compared to not compiling in > > uclamp? I suppose the important bit is that we're not seeing regressions > > anymore, but still. > > > > I haven't reviewed the series in depth because from your review, another > version is likely in the works. However, it is not that unusual to > see small fluctuations like this that are counter-intuitive. The report > indicates the difference is likely outside of the noise with * around the > percentage difference instead of () but it could be small boot-to-boot > variance, differences in code layout, slight differences in slab usage > patterns etc. The definitive evidence that uclamp overhead is no there > is whether the uclamp functions show up in annotated profiles or not.
The diff between nouclamp and uclamp-static-key (disabling uclamp in fast path)
8.73% -1.55% [kernel.kallsyms] [k] try_to_wake_up 0.07% +0.04% [kernel.kallsyms] [k] deactivate_task 0.13% -0.02% [kernel.kallsyms] [k] activate_task
The diff between nouclamp and uclamp-static-key (uclamp actively used in the fast path)
8.73% -0.72% [kernel.kallsyms] [k] try_to_wake_up 0.13% +0.39% [kernel.kallsyms] [k] activate_task 0.07% +0.38% [kernel.kallsyms] [k] deactivate_task
I will include these numbers in the commit message in v2.
Thanks
-- Qais Yousef
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