linux-kernel - Re: [PATCH] target/file: don't zero iter before iov_iter

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Date:   Mon, 11 Jan 2021 02:06:11 +0000
From:   Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>
To:     Pavel Begunkov <asml.silence@...il.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>
CC:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] target/file: don't zero iter before iov_iter_bvec

On 1/9/21 13:29, Pavel Begunkov wrote:
> On 09/01/2021 20:52, Chaitanya Kulkarni wrote:
>> On 1/9/21 12:40, Pavel Begunkov wrote:
>>> I expect you won't find any, but such little things can pile up
>>> into a not-easy-to-spot overhead over time.
>> That is what I suspected with the resulting assembly. The commit log
>> needs to document that there is no direct impact on the performance
> It's obvious that 3-4 extra mov $0 off(%reg) won't change performance
> but still hasn't been formally confirmed ...
This is obvious for you and me since we spent time into looking into
resulting assembly not every reviewer is expected to do that see [1].
>
>> which can be seen with this patch, but this is nice to have
> ... so if you don't mind, I won't be resending just for that.
As per commit log guidelines [1] you have to quantify the optimization.

Since you cannot quantify the optimization modify the commit log explaining
that there is not significant performance benefit observe.
> -- Pavel Begunkov
[1] https://www.kernel.org/doc/html/v4.10/process/submitting-patches.html