linux-kernel - Re: [PATCH 3/4] blk-mq: implement hybrid poll mode for sync O

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Message-ID: <20161102145459.GD13964@lst.de>
Date:   Wed, 2 Nov 2016 15:54:59 +0100
From:   Christoph Hellwig <hch@....de>
To:     Jens Axboe <axboe@...com>
Cc:     axboe@...nel.dk, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, hch@....de
Subject: Re: [PATCH 3/4] blk-mq: implement hybrid poll mode for sync
        O_DIRECT

On Tue, Nov 01, 2016 at 03:05:24PM -0600, Jens Axboe wrote:
> This patch enables a hybrid polling mode. Instead of polling after IO
> submission, we can induce an artificial delay, and then poll after that.
> For example, if the IO is presumed to complete in 8 usecs from now, we
> can sleep for 4 usecs, wake up, and then do our polling. This still puts
> a sleep/wakeup cycle in the IO path, but instead of the wakeup happening
> after the IO has completed, it'll happen before. With this hybrid
> scheme, we can achieve big latency reductions while still using the same
> (or less) amount of CPU.
> 
> Signed-off-by: Jens Axboe <axboe@...com>

This looks very nice.  I'll need to run some tests before giving the
formal ACK, though.