linux-kernel - Re: [RFC] blkio_delay_total is calculated mistakenly

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Message-ID: <CA+scX6nb-7hvFecBn8m1rbf0y3n7goJuHWOiwbrKTvS+ysjh2w@mail.gmail.com>
Date:   Thu, 2 Mar 2017 08:51:36 -0500
From:   Weiwei Jia <harrynjit@...il.com>
To:     Balbir Singh <bsingharora@...il.com>
Cc:     linux-kernel@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [RFC] blkio_delay_total is calculated mistakenly

Ping?

Can anyone please add some comments for this change? Thank you.

Best,
Weiwei Jia

On Tue, Feb 14, 2017 at 8:27 PM, Weiwei Jia <harrynjit@...il.com> wrote:
> Hi,
>
> When I read Linux Kernel source codes about how "blkio_delay_total"
> (delay waiting for synchronous block I/O to complete for one task) is
> calculated in Linux/kernel/delayacct.c file [1], I find that
> "blkio_delay_total" adds "task->delays->blkio_delay" to be the total
> delay time for one task to wait for synchronous I/O dynamically but
> "tsk->delays->blkio_delay" has already been calculated as the total
> delay time that one task is waiting for synchronous I/O [2]
> dynamically. I think "blkio_delay_total" should not add
> "task->delays->blkio_delay" since "task->delays->blkio_delay" is
> already the total delay time we want.
>
> Am I missing anything?
>
> BTW, the patch in the attachment may solve this problem if I don't
> miss anything. Thank you.
>
>
> [1] http://lxr.free-electrons.com/source/kernel/delayacct.c?v=4.7#L121
> [2] http://lxr.free-electrons.com/source/kernel/delayacct.c?v=4.7#L52
>
> Thanks,
> Weiwei Jia