Re: [PATCH v6 0/4] sched/fair: Improve scan efficiency of SIS

[Abel Wu]

Hi Prateek, thanks again for your detailed test!

On 11/22/22 7:28 PM, K Prateek Nayak wrote:
> Hello Abel,
>
> Following are the results for hackbench with larger number of
> groups, ycsb-mongodb, Spec-JBB, and unixbench. Apart for
> a regression in unixbench spawn in NPS2 and NPS4 mode and
> unixbench syscall in NPs2 mode, everything looks good.
>
> ...
>
> -> unixbench-syscall
>
> o NPS4
>
> kernel:                             tip                  sis_core
> Min       unixbench-syscall-1    2971799.80 (   0.00%)  2979335.60 (  -0.25%)
> Min       unixbench-syscall-512  7824196.90 (   0.00%)  8155610.20 (  -4.24%)
> Amean     unixbench-syscall-1    2973045.43 (   0.00%)  2982036.13 *  -0.30%*
> Amean     unixbench-syscall-512  7826302.17 (   0.00%)  8173026.57 *  -4.43%*   <-- Regression in syscall for larger worker count
> CoeffVar  unixbench-syscall-1          0.04 (   0.00%)        0.09 (-139.63%)
> CoeffVar  unixbench-syscall-512        0.03 (   0.00%)        0.20 (-701.13%)
>
>
> -> unixbench-spawn
>
> o NPS1
>
> kernel:                             tip                  sis_core
> Min       unixbench-spawn-1       6536.50 (   0.00%)     6000.30 (  -8.20%)
> Min       unixbench-spawn-512    72571.40 (   0.00%)    70829.60 (  -2.40%)
> Hmean     unixbench-spawn-1       6811.16 (   0.00%)     7016.11 (   3.01%)
> Hmean     unixbench-spawn-512    72801.77 (   0.00%)    71012.03 *  -2.46%*
> CoeffVar  unixbench-spawn-1          3.69 (   0.00%)       13.52 (-266.69%)
> CoeffVar  unixbench-spawn-512        0.27 (   0.00%)        0.22 (  18.25%)
>
> o NPS2
>
> kernel:                             tip                  sis_core
> Min       unixbench-spawn-1       7042.20 (   0.00%)     7078.70 (   0.52%)
> Min       unixbench-spawn-512    85571.60 (   0.00%)    77362.60 (  -9.59%)
> Hmean     unixbench-spawn-1       7199.01 (   0.00%)     7276.55 (   1.08%)
> Hmean     unixbench-spawn-512    85717.77 (   0.00%)    77923.73 *  -9.09%*     <-- Regression in spawn test for larger worker count
> CoeffVar  unixbench-spawn-1          3.50 (   0.00%)        3.30 (   5.70%)
> CoeffVar  unixbench-spawn-512        0.20 (   0.00%)        0.82 (-304.88%)
>
> o NPS4
>
> kernel:                             tip                  sis_core
> Min       unixbench-spawn-1       7521.90 (   0.00%)     8102.80 (   7.72%)
> Min       unixbench-spawn-512    84245.70 (   0.00%)    73074.50 ( -13.26%)
> Hmean     unixbench-spawn-1       7659.12 (   0.00%)     8645.19 *  12.87%*
> Hmean     unixbench-spawn-512    84908.77 (   0.00%)    73409.49 * -13.54%*     <-- Regression in spawn test for larger worker count
> CoeffVar  unixbench-spawn-1          1.92 (   0.00%)        5.78 (-200.56%)
> CoeffVar  unixbench-spawn-512        0.76 (   0.00%)        0.41 (  46.58%)
>
> ...
>
> For unixbench regressions, I do not see anything obvious jump up
> in perf traces captureed with IBS. top shows over 99% utilization
> which would ideally mean there are not many updates to the mask.
> I'll take some more look at the spawn test case and get back to you.

These regressions seems to be common in full parallel tests. I
guess it might be due to over updating the idle cpumask when LLC
is overloaded which is not necessary if SIS_UTIL enabled, but I
need to dig it further. Maybe the rq avg_idle or nr_idle_scan need
to be taken into consideration as well. Thanks for providing these
important information.

> ~~~~~~~~~~~~~
> ~ Hackbench ~
> ~~~~~~~~~~~~~
>
> $ perf bench sched messaging -p -l 50000 -g <groups>
>
> o NPS1
>
> kernel:               tip                     sis_core
> 32-groups:         6.20 (0.00 pct)         5.86 (5.48 pct)
> 64-groups:        16.55 (0.00 pct)        15.21 (8.09 pct)
> 128-groups:       42.57 (0.00 pct)        34.63 (18.65 pct)
> 256-groups:       71.69 (0.00 pct)        67.11 (6.38 pct)
> 512-groups:      108.48 (0.00 pct)       110.23 (-1.61 pct)
>
> o NPS2
>
> kernel:                tip                     sis_core
> 32-groups:         6.56 (0.00 pct)         5.60 (14.63 pct)
> 64-groups:        15.74 (0.00 pct)        14.45 (8.19 pct)
> 128-groups:       39.93 (0.00 pct)        35.33 (11.52 pct)
> 256-groups:       74.49 (0.00 pct)        69.65 (6.49 pct)
> 512-groups:      112.22 (0.00 pct)       113.75 (-1.36 pct)
>
> o NPS4:
>
> kernel:               tip                     sis_core
> 32-groups:         9.48 (0.00 pct)         5.64 (40.50 pct)
> 64-groups:        15.38 (0.00 pct)        14.13 (8.12 pct)
> 128-groups:       39.93 (0.00 pct)        34.47 (13.67 pct)
> 256-groups:       75.31 (0.00 pct)        67.98 (9.73 pct)
> 512-groups:      115.37 (0.00 pct)       111.15 (3.65 pct)
>
> Note: Hackbench with 32-groups show run to run variation
> on tip but is more stable with sis_core. Hackbench for
> 64-groups and beyond is stable on both kernels.
The result is consistent with mine except 512-groups which I
didn't test. The 512-groups test may have the same problem
aforementioned.

Thanks & Regards,
	Abel