linux-kernel - Re: [memcg] 45208c9105: aim7.jobs-per-min -14.0% regression

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Date:   Mon, 13 Sep 2021 09:42:46 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Feng Tang <feng.tang@...el.com>, Hillf Danton <hdanton@...a.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Xing Zhengjun <zhengjun.xing@...ux.intel.com>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: [memcg] 45208c9105: aim7.jobs-per-min -14.0% regression

Hello,

On Mon, Sep 13, 2021 at 12:40:06PM -0700, Shakeel Butt wrote:
> I did one more experiment with same workload but with system_wq
> instead system_unbound_wq and there is clear difference in profile:
> 
> With system_unbound_wq:
> -    4.63%     0.33%  mmap  [kernel.kallsyms]  [k] queue_work_on
>      4.29% queue_work_on
>       - __queue_work
>          - 3.45% wake_up_process
>             - try_to_wake_up
>                - 2.46% ttwu_queue
>                   - 1.66% ttwu_do_activate
>                      - 1.14% activate_task
>                         - 0.97% enqueue_task_fair
>                              enqueue_entity
> 
> With system_wq:
> -    1.36%     0.06%  mmap  [kernel.kallsyms]  [k] queue_work_on
>      1.30% queue_work_on
>       - __queue_work
>          - 1.03% wake_up_process
>             - try_to_wake_up
>                - 0.97% ttwu_queue
>                     0.66% ttwu_do_activate
> 
> Tejun, is this expected? i.e. queuing work on system_wq has a
> different performance impact than on system_unbound_wq?

Yes, system_unbound_wq is putting the work item on the global shared
workqueue while the system_wq is per-cpu, so on a loaded system, overhead
difference showing up isn't too surprising.

Thanks.

-- 
tejun