linux-kernel - Re: [PATCH 1/4] block: add scalable completion tracking of requests

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Date:   Wed, 2 Nov 2016 15:59:48 +0100
From:   Christoph Hellwig <hch@....de>
To:     Jens Axboe <axboe@...com>
Cc:     Christoph Hellwig <hch@....de>, axboe@...nel.dk,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH 1/4] block: add scalable completion tracking of requests

On Wed, Nov 02, 2016 at 08:55:16AM -0600, Jens Axboe wrote:
> On 11/02/2016 08:52 AM, Christoph Hellwig wrote:
>> On Tue, Nov 01, 2016 at 03:05:22PM -0600, Jens Axboe wrote:
>>> For legacy block, we simply track them in the request queue. For
>>> blk-mq, we track them on a per-sw queue basis, which we can then
>>> sum up through the hardware queues and finally to a per device
>>> state.
>>
>> what is the use case for the legacy request tracking?
>
> Buffered writeback code uses the same base. Additionally, it could
> replace some user space tracking for latency outliers that people are
> currently running.

Ok.