linux-kernel - Re: [linus:master] [mm] f1a7941243: unixbench.score -19.2% regression

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Date:   Mon, 27 Feb 2023 06:35:31 +0000
From:   "Yin, Fengwei" <fengwei.yin@...el.com>
To:     "shakeelb@...gle.com" <shakeelb@...gle.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "tj@...nel.org" <tj@...nel.org>,
        "dennis@...nel.org" <dennis@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     lkp <lkp@...el.com>,
        "zhengjun.xing@...ux.intel.com" <zhengjun.xing@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Tang, Feng" <feng.tang@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "Sang, Oliver" <oliver.sang@...el.com>,
        "linux-trace-kernel@...r.kernel.org" 
        <linux-trace-kernel@...r.kernel.org>,
        "oe-lkp@...ts.linux.dev" <oe-lkp@...ts.linux.dev>
Subject: Re: [linus:master] [mm] f1a7941243: unixbench.score -19.2% regression

Hi Andrew, Shakeel,

On Tue, 2023-01-31 at 10:26 -0800, Shakeel Butt wrote:
> +per-cpu memory maintainers for FYI.
> 
> Thread started at
> https://lore.kernel.org/linux-mm/202301301057.e55dad5b-oliver.sang@intel.com/
> 
> On Mon, Jan 30, 2023 at 9:57 PM Shakeel Butt <shakeelb@...gle.com>
> wrote:
> > 
> [...]
> > > 
> > > We could cut down the number of calls to pcpu_alloc() by a factor
> > > of 4
> > > by having a pcpu_alloc_bulk() that would allocate all four RSS
> > > counters
> > > at once.
> > > 
> > > Just throwing out ideas ...
> > 
> > Thanks, I will take a stab at pcpu_alloc_bulk() and will share the
> > result tomorrow.
> > 
> 
> OK, not a one day effort.
> 
> Andrew, which option do you prefer?
> 
> 1. Keep the patches as the test workload (fork ping pong) is not a
> representative of real world workload and work on improving
> pcpu_alloc() for 6.4+.
> 
> 2. Revert the patches for now, improve pcpu_alloc() and re-introduce
> the patches once we confirm that fork-ping-pong is not regressed
> anymore.
This performance regression still can be reproduced on latest master
branch. So we took option1 here. Right? Thanks.

Regards
Yin, Fengwei

> 
> thanks,
> Shakeel