linux-kernel - Re: [LKP] Re: [mm/memcg] bd0b230fe1: will-it-scale.per_process

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Date:   Wed, 4 Nov 2020 09:15:46 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Xing Zhengjun <zhengjun.xing@...ux.intel.com>
Cc:     Rong Chen <rong.a.chen@...el.com>,
        Waiman Long <longman@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Chris Down <chris@...isdown.name>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Tejun Heo <tj@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Yafang Shao <laoar.shao@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        lkp@...el.com, zhengjun.xing@...el.com
Subject: Re: [LKP] Re: [mm/memcg] bd0b230fe1: will-it-scale.per_process_ops
 -22.7% regression

On Wed 04-11-20 09:20:04, Xing Zhengjun wrote:
> 
> 
> On 11/2/2020 6:02 PM, Michal Hocko wrote:
> > On Mon 02-11-20 17:53:14, Rong Chen wrote:
> > > 
> > > 
> > > On 11/2/20 5:27 PM, Michal Hocko wrote:
> > > > On Mon 02-11-20 17:15:43, kernel test robot wrote:
> > > > > Greeting,
> > > > > 
> > > > > FYI, we noticed a -22.7% regression of will-it-scale.per_process_ops due to commit:
> > > > > 
> > > > > 
> > > > > commit: bd0b230fe14554bfffbae54e19038716f96f5a41 ("mm/memcg: unify swap and memsw page counters")
> > > > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> > > > I really fail to see how this can be anything else than a data structure
> > > > layout change. There is one counter less.
> > > > 
> > > > btw. are cgroups configured at all? What would be the configuration?
> > > 
> > > Hi Michal,
> > > 
> > > We used the default configure of cgroups, not sure what configuration you
> > > want,
> > > could you give me more details? and here is the cgroup info of will-it-scale
> > > process:
> > > 
> > > $ cat /proc/3042/cgroup
> > > 12:hugetlb:/
> > > 11:memory:/system.slice/lkp-bootstrap.service
> > 
> > OK, this means that memory controler is enabled and in use. Btw. do you
> > get the original performance if you add one phony page_counter after the
> > union?
> > 
> I add one phony page_counter after the union and re-test, the regression
> reduced to -1.2%. It looks like the regression caused by the data structure
> layout change.

Thanks for double checking. Could you try to cache align the
page_counter struct? If that helps then we should figure which counters
acks against each other by adding the alignement between the respective
counters. 

> =========================================================================================
> tbox_group/testcase/rootfs/kconfig/compiler/nr_task/mode/test/cpufreq_governor/ucode/debug-setup:
> 
> lkp-hsw-4ex1/will-it-scale/debian-10.4-x86_64-20200603.cgz/x86_64-rhel-8.3/gcc-9/50%/process/page_fault2/performance/0x16/test1
> 
> commit:
>   8d387a5f172f26ff8c76096d5876b881dec6b7ce
>   bd0b230fe14554bfffbae54e19038716f96f5a41
>   b3233916ab0a883e1117397e28b723bd0e4ac1eb (debug patch add one phony
> page_counter after the union)
> 
> 8d387a5f172f26ff bd0b230fe14554bfffbae54e190 b3233916ab0a883e1117397e28b
> ---------------- --------------------------- ---------------------------
>          %stddev     %change         %stddev     %change         %stddev
>              \          |                \          |                \
>     187632           -22.8%     144931            -1.2%     185391
> will-it-scale.per_process_ops
>   13509525           -22.8%   10435073            -1.2%   13348181
> will-it-scale.workload
> 
> 
> 
> -- 
> Zhengjun Xing

-- 
Michal Hocko
SUSE Labs