Re: [RFC PATCH 1 1/1] sched/numa: Hot VMA and shared VMA optimization

[Raghavendra K T]

On 6/25/2024 7:50 PM, Chen Yu wrote:
> Hi Raghavendra,
>
> On 2024-03-22 at 19:11:12 +0530, Raghavendra K T wrote:
> > Optimizations are based on history of PIDs accessing VMA.
> >
> > - Increase tasks' access history windows (PeterZ) from 2 to 4.
> > ( This patch is from Peter Zijlstra <peterz@xxxxxxxxxxxxx>)
> >
> > Idea: A task is allowed to scan a VMA if:
> > - VMA was very recently accessed as indicated by the latest
> >    access PIDs information (hot VMA).
> > - VMA is shared by more than 2 tasks. Here whole history of VMA's
> > access PIDs is considered using bitmap_weight().
> >
> > Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxx>
> > ---
> > I will split the patset and post if we find this pathset useful
> > going further. First patch is from PeterZ.
>
> This is a good direction I think. We did an initial test using autonumabench
> THREADLOCAL on a 240 CPUs 2 nodes system. It seems that this patch does not
> show obvious difference, but it shows a more stable result(less run-to-run
> variance). We'll enable the Sub-Numa-Cluster to see if there is any difference.
> My understanding is that, if we can extend the NR_ACCESS_PID_HIST further,
> the THREADLOCAL could see more benefits, as each thread has its own VMA. Or maybe
> make the length of VMA access history adaptive(rather than a fixed 4) could be
> more flexible.
>                                            numa_scan_orig    numa_scan_4_history
> Min       syst-NUMA01_THREADLOCAL      388.47 (   0.00%)      397.43 (  -2.31%)
> Min       elsp-NUMA01_THREADLOCAL       40.27 (   0.00%)       38.94 (   3.30%)
> Amean     syst-NUMA01_THREADLOCAL      467.62 (   0.00%)      459.10 (   1.82%)
> Amean     elsp-NUMA01_THREADLOCAL       42.20 (   0.00%)       44.84 (  -6.26%)
> Stddev    syst-NUMA01_THREADLOCAL       74.11 (   0.00%)       60.90 (  17.81%)
> CoeffVar  syst-NUMA01_THREADLOCAL       15.85 (   0.00%)       13.27 (  16.29%)
> Max       syst-NUMA01_THREADLOCAL      535.36 (   0.00%)      519.21 (   3.02%)
> Max       elsp-NUMA01_THREADLOCAL       43.96 (   0.00%)       56.33 ( -28.14%)
> BAmean-50 syst-NUMA01_THREADLOCAL      388.47 (   0.00%)      397.43 (  -2.31%)
> BAmean-50 elsp-NUMA01_THREADLOCAL       40.27 (   0.00%)       38.94 (   3.30%)
> BAmean-95 syst-NUMA01_THREADLOCAL      433.75 (   0.00%)      429.05 (   1.08%)
> BAmean-95 elsp-NUMA01_THREADLOCAL       41.31 (   0.00%)       39.09 (   5.39%)
> BAmean-99 syst-NUMA01_THREADLOCAL      433.75 (   0.00%)      429.05 (   1.08%)
> BAmean-99 elsp-NUMA01_THREADLOCAL       41.31 (   0.00%)       39.09 (   5.39%)

Thanks for the test and report. I will split the patches and also test 
for N=6,8.
(on top of your patch perhaps to make sure we have benefits further).

Making adaptive may be little difficult. How to assess which size is 
doing better dynamically seems to be little hard to imagine for me. (/me
Need to think here)

Thanks and Regards
- Raghu