Re: [mm] 2d146aa3aa: vm-scalability.throughput -36.4% regression

[Feng Tang]

On Wed, Sep 01, 2021 at 07:23:24PM -0700, Andi Kleen wrote:
> 
> On 9/1/2021 6:35 PM, Feng Tang wrote:
> >On Wed, Sep 01, 2021 at 08:12:24AM -0700, Andi Kleen wrote:
> >>Feng Tang <feng.tang@xxxxxxxxx> writes:
> >>>Yes, the tests I did is no matter where the 128B padding is added, the
> >>>performance can be restored and even improved.
> >>I wonder if we can find some cold, rarely accessed, data to put into the
> >>padding to not waste it. Perhaps some name strings? Or the destroy
> >>support, which doesn't sound like its commonly used.
> >Yes, I tried to move 'destroy_work', 'destroy_rwork' and 'parent' over
> >before the 'refcnt' together with some padding, it restored the performance
> >to about 10~15% regression. (debug patch pasted below)
> >
> >But I'm not sure if we should use it, before we can fully explain the
> >regression.
> 
> Narrowing it down to a single prefetcher seems good enough to me. The
> behavior of the prefetchers is fairly complicated and hard to predict, so I
> doubt you'll ever get a 100% step by step explanation.

Yes, I'm afriad so, given that the policy/algorithm used by perfetcher
keeps changing from generation to generation.

I will test the patch more with other benchmarks.

Thanks,
Feng

> 
> -Andi
>