linux-kernel - Re: [PATCH] block: add iostat counters for flush requests

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Message-ID: <20191121160430.GJ6211@magnolia>
Date:   Thu, 21 Nov 2019 08:04:30 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org,
        Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
Subject: Re: [PATCH] block: add iostat counters for flush requests

On Thu, Nov 21, 2019 at 08:56:14AM -0700, Jens Axboe wrote:
> On 11/21/19 3:40 AM, Konstantin Khlebnikov wrote:
> > Requests that triggers flushing volatile writeback cache to disk (barriers)
> > have significant effect to overall performance.
> > 
> > Block layer has sophisticated engine for combining several flush requests
> > into one. But there is no statistics for actual flushes executed by disk.
> > Requests which trigger flushes usually are barriers - zero-size writes.
> > 
> > This patch adds two iostat counters into /sys/class/block/$dev/stat and
> > /proc/diskstats - count of completed flush requests and their total time.
> 
> This makes sense to me, and the "recent" discard addition already proved
> that we're fine extending with more fields. Unless folks object, I'd be
> happy to queue this up for 5.5.

Looks like a good addition to /me... :)

--D

> -- 
> Jens Axboe
>