Messages in this thread | | | Date | Mon, 27 Sep 2021 12:17:30 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 2/2] sched/fair: Scale wakeup granularity relative to nr_running |
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On Thu, Sep 23, 2021 at 02:41:06PM +0200, Vincent Guittot wrote: > On Thu, 23 Sept 2021 at 11:22, Mike Galbraith <efault@gmx.de> wrote: > > > > On Thu, 2021-09-23 at 10:40 +0200, Vincent Guittot wrote: > > > > > > a 100us value should even be enough to fix Mel's problem without > > > impacting common wakeup preemption cases. > > > > It'd be nice if it turn out to be something that simple, but color me > > skeptical. I've tried various preemption throttling schemes, and while > > Let's see what the results will show. I tend to agree that this will > not be enough to cover all use cases and I don't see any other way to > cover all cases than getting some inputs from the threads about their > latency fairness which bring us back to some kind of latency niceness > value >
Unfortunately, I didn't get a complete set of results but enough to work with. The missing tests have been requeued. The figures below are based on a single-socket Skylake machine with 8 CPUs as it had the most set of results and is the basic case.
The reported kernels are
vanilla: vanilla 5.15-rc1 sched-scalewakegran-v2r4: My patch sched-moveforward-v1r1: Vincent's patch
hackbench-process-pipes 5.15.0-rc1 5.15.0-rc1 5.15.0-rc1 vanilla sched-scalewakegran-v2r4 sched-moveforward-v1r1 Amean 1 0.3253 ( 0.00%) 0.3330 ( -2.36%) 0.3257 ( -0.10%) Amean 4 0.8300 ( 0.00%) 0.7570 ( 8.80%) 0.7560 ( 8.92%) Amean 7 1.1003 ( 0.00%) 1.1457 * -4.12%* 1.1163 ( -1.45%) Amean 12 1.7263 ( 0.00%) 1.6393 * 5.04%* 1.5963 * 7.53%* Amean 21 3.0063 ( 0.00%) 2.6590 * 11.55%* 2.4487 * 18.55%* Amean 30 4.2323 ( 0.00%) 3.5657 * 15.75%* 3.3410 * 21.06%* Amean 48 6.5657 ( 0.00%) 5.4180 * 17.48%* 5.0857 * 22.54%* Amean 79 10.4867 ( 0.00%) 8.4357 * 19.56%* 7.9563 * 24.13%* Amean 110 14.8880 ( 0.00%) 11.0423 * 25.83%* 10.7407 * 27.86%* Amean 141 19.2083 ( 0.00%) 14.0820 * 26.69%* 13.3780 * 30.35%* Amean 172 23.4847 ( 0.00%) 16.9880 * 27.66%* 16.4293 * 30.04%* Amean 203 27.3763 ( 0.00%) 20.2480 * 26.04%* 19.6430 * 28.25%* Amean 234 31.3707 ( 0.00%) 23.2477 * 25.89%* 22.8287 * 27.23%* Amean 265 35.4663 ( 0.00%) 26.2483 * 25.99%* 25.8683 * 27.06%* Amean 296 39.2380 ( 0.00%) 29.4237 * 25.01%* 28.8727 * 26.42%*
For hackbench, either Vincent or my patch has a similar impact.
tbench4 5.15.0-rc1 5.15.0-rc1 5.15.0-rc1 vanillasched-scalewakegran-v2r4 sched-moveforward-v1r1 Hmean 1 598.71 ( 0.00%) 608.31 * 1.60%* 586.05 * -2.11%* Hmean 2 1096.74 ( 0.00%) 1110.07 * 1.22%* 1106.70 * 0.91%* Hmean 4 1529.35 ( 0.00%) 1531.20 * 0.12%* 1551.11 * 1.42%* Hmean 8 2824.32 ( 0.00%) 2847.96 * 0.84%* 2684.21 * -4.96%* Hmean 16 2573.30 ( 0.00%) 2591.77 * 0.72%* 2445.41 * -4.97%* Hmean 32 2518.77 ( 0.00%) 2532.70 * 0.55%* 2409.30 * -4.35%*
For tbench, it's ok for lower thread counts for 8 threads (machine overloaded), Vincent's patch regresses slightly. With these test runs, I don't have detailed information as to why but the most likely solution is that preemption gets disabled prematurely.
specjbb 5.15.0-rc1 5.15.0-rc1 5.15.0-rc1 vanillasched-scalewakegran-v2r4 sched-moveforward-v1r1 Hmean tput-1 71199.00 ( 0.00%) 69492.00 * -2.40%* 71126.00 * -0.10%* Hmean tput-2 154478.00 ( 0.00%) 146060.00 * -5.45%* 153073.00 * -0.91%* Hmean tput-3 211889.00 ( 0.00%) 209386.00 * -1.18%* 219434.00 * 3.56%* Hmean tput-4 257842.00 ( 0.00%) 248012.00 * -3.81%* 262903.00 * 1.96%* Hmean tput-5 253506.00 ( 0.00%) 242511.00 * -4.34%* 250828.00 * -1.06%* Hmean tput-6 246202.00 ( 0.00%) 236480.00 * -3.95%* 244236.00 * -0.80%* Hmean tput-7 241133.00 ( 0.00%) 230905.00 * -4.24%* 237619.00 * -1.46%* Hmean tput-8 237983.00 ( 0.00%) 230010.00 * -3.35%* 235275.00 * -1.14%*
For specjbb, it's different again, Vincent's patch is better for the overloaded case but both patches show light regressions.
-- Mel Gorman SUSE Labs
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