Messages in this thread | | | Subject | Re: [PATCH v6 0/2] sched: Optionally skip uclamp logic in fast path | From | Lukasz Luba <> | Date | Wed, 1 Jul 2020 17:32:09 +0100 |
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Hi Qais,
On 6/30/20 12:21 PM, Qais Yousef wrote: > This series attempts to address the report that uclamp logic could be expensive > sometimes and shows a regression in netperf UDP_STREAM under certain > conditions. > > The first patch is a fix for how struct uclamp_rq is initialized which is > required by the 2nd patch which contains the real 'fix'. > > Worth noting that the root cause of the overhead is believed to be system > specific or related to potential certain code/data layout issues, leading to > worse I/D $ performance. > > Different systems exhibited different behaviors and the regression did > disappear in certain kernel version while attempting to reporoduce. > > More info can be found here: > > https://lore.kernel.org/lkml/20200616110824.dgkkbyapn3io6wik@e107158-lin/ > > Having the static key seemed the best thing to do to ensure the effect of > uclamp is minimized for kernels that compile it in but don't have a userspace > that uses it, which will allow distros to distribute uclamp capable kernels by > default without having to compromise on performance for some systems that could > be affected. > > Changes in v6: > * s/uclamp_is_enabled/uclamp_is_used/ + add comment > * Improve the bailout condition for the case where we could end up with > unbalanced call of uclamp_rq_dec_id() > * Clarify some comments. >
I've tried this v6 series with mmtest netperf-udp (30x each UDP size) - the results are good.
v5.7-rc7-base-noucl v5.7-rc7-ucl-tsk-nofix v5.7-rc7-ucl-tsk-grp-fix_v6 Hmean send-64 62.15 ( 0.00%) 59.65 * -4.02%* 65.87 * 5.99%* Hmean send-128 122.88 ( 0.00%) 119.37 * -2.85%* 131.76 * 7.23%* Hmean send-256 244.85 ( 0.00%) 234.26 * -4.32%* 259.87 * 6.14%* Hmean send-1024 919.24 ( 0.00%) 880.67 * -4.20%* 975.48 * 6.12%* Hmean send-2048 1689.45 ( 0.00%) 1647.54 * -2.48%* 1797.23 * 6.38%* Hmean send-3312 2542.36 ( 0.00%) 2485.23 * -2.25%* 2665.69 * 4.85%* Hmean send-4096 2935.69 ( 0.00%) 2861.09 * -2.54%* 3087.79 * 5.18%* Hmean send-8192 4800.35 ( 0.00%) 4680.09 * -2.51%* 4966.50 * 3.46%* Hmean send-16384 7473.66 ( 0.00%) 7349.60 * -1.66%* 7598.49 * 1.67%* Hmean recv-64 62.15 ( 0.00%) 59.65 * -4.03%* 65.86 * 5.97%* Hmean recv-128 122.88 ( 0.00%) 119.37 * -2.85%* 131.76 * 7.23%* Hmean recv-256 244.84 ( 0.00%) 234.26 * -4.32%* 259.80 * 6.11%* Hmean recv-1024 919.24 ( 0.00%) 880.67 * -4.20%* 975.42 * 6.11%* Hmean recv-2048 1689.44 ( 0.00%) 1647.54 * -2.48%* 1797.18 * 6.38%* Hmean recv-3312 2542.36 ( 0.00%) 2485.23 * -2.25%* 2665.53 * 4.84%* Hmean recv-4096 2935.69 ( 0.00%) 2861.09 * -2.54%* 3087.79 * 5.18%* Hmean recv-8192 4800.35 ( 0.00%) 4678.15 * -2.55%* 4966.48 * 3.46%* Hmean recv-16384 7473.63 ( 0.00%) 7349.52 * -1.66%* 7597.90 * 1.66%*
You can add:
Tested-by: Lukasz Luba <lukasz.luba@arm.com>
Regards, Lukasz
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