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Subject: Re: [PATCH] block: add iostat counters for flush requests
To:     Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org
Cc:     linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
        Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
References: <157433282607.7928.5202409984272248322.stgit@buzz>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <ff971ff6-9a10-c3f1-107d-4f7d378e8755@kernel.dk>
Date:   Thu, 21 Nov 2019 08:56:14 -0700
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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.

-- 
Jens Axboe