linux-kernel - Re: [PATCH] blk: optimization for classic polling

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Message-ID: <35a2d52e-dd40-d130-85d9-5f3ffe0d28af@kernel.dk>
Date:   Tue, 20 Feb 2018 12:37:07 -1000
From:   Jens Axboe <axboe@...nel.dk>
To:     Peter Zijlstra <peterz@...radead.org>,
        Nitesh Shetty <nj.shetty@...sung.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        viro@...iv.linux.org.uk, linux-block@...r.kernel.org,
        linux-nvme@...ts.infradead.org, joshi.k@...sung.com
Subject: Re: [PATCH] blk: optimization for classic polling

On 2/20/18 3:21 AM, Peter Zijlstra wrote:
> On Sun, May 30, 2083 at 09:51:06AM +0530, Nitesh Shetty wrote:
>> This removes the dependency on interrupts to wake up task. Set task
>> state as TASK_RUNNING, if need_resched() returns true,
>> while polling for IO completion.
>> Earlier, polling task used to sleep, relying on interrupt to wake it up.
>> This made some IO take very long when interrupt-coalescing is enabled in
>> NVMe.
> 
> This is a horrible Changelog.. it does not in fact explain why the patch
> works or is correct.

Yeah, that should have been improved.

> Also, set_current_state(TASK_RUNNING) is dodgy (similarly in
> __blk_mq_poll), why do you need that memory barrier?

I pointed that out in the review, and v2 fixed it. v2 is the
one that got merged.

-- 
Jens Axboe