From: axboe@fb.com (Jens Axboe)
Subject: blk-mq merge flags
Date: Tue, 15 Mar 2016 15:13:26 -0700 [thread overview]
Message-ID: <56E88906.2060205@fb.com> (raw)
In-Reply-To: <20160315160833.GA21474@infradead.org>
On 03/15/2016 09:08 AM, Christoph Hellwig wrote:
> Jens, Keith -
>
> any comments? I think the lack of BLK_MQ_F_SG_MERGE for nvme
> is rather harmful at the moment, as I get much better request
> packing with it. I'd rather fix this in the block layer, but
> if that's not ok I can also send a pure NVMe patch.
We can default to merging, and have drivers opt out, if they need to.
NVMe is probably the only one that doesn't set the flag currently, so
the net effect of the two different approaches would be the same. We'll
have a slightly higher CPU overhead without a perf win for workloads
that don't get merging, but overall it's always a win if we can merge
commands. So a better default, I think, even for nvme.
--
Jens Axboe
next prev parent reply other threads:[~2016-03-15 22:13 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-02 17:07 [for 4.5] fix regression for large NVMe user command Christoph Hellwig
2016-03-02 17:07 ` [PATCH 1/5] nvme: also set BLK_MQ_F_SHOULD_MERGE for the admin queue Christoph Hellwig
2016-03-02 17:35 ` Sagi Grimberg
2016-03-02 18:15 ` Keith Busch
2016-03-02 21:17 ` Christoph Hellwig
2016-03-02 23:55 ` Ming Lei
[not found] ` <20160303084609.GA14051@lst.de>
2016-03-03 11:24 ` blk-mq merge flags Ming Lei
2016-03-03 11:59 ` Christoph Hellwig
2016-03-15 16:08 ` Christoph Hellwig
2016-03-15 22:13 ` Jens Axboe [this message]
2016-03-02 20:01 ` [PATCH 1/5] nvme: also set BLK_MQ_F_SHOULD_MERGE for the admin queue Jens Axboe
2016-03-02 17:07 ` [PATCH 2/5] nvme: set queue limits " Christoph Hellwig
2016-03-02 19:10 ` Keith Busch
2016-03-02 17:07 ` [PATCH 3/5] nvme: fix max_segments integer truncation Christoph Hellwig
2016-03-02 18:27 ` Keith Busch
2016-03-02 17:07 ` [PATCH 4/5] block: fix blk_rq_get_max_sectors for driver private requests Christoph Hellwig
2016-03-02 19:17 ` Keith Busch
2016-03-02 21:18 ` Christoph Hellwig
2016-03-02 22:16 ` Jens Axboe
2016-03-02 17:07 ` [PATCH 5/5] block: support large requests in blk_rq_map_user_iov Christoph Hellwig
2016-03-02 19:34 ` Keith Busch
2016-03-02 21:20 ` Christoph Hellwig
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