From: Jens Axboe <axboe@kernel.dk>
To: Ming Lei <ming.lei@canonical.com>, Shaohua Li <shli@fb.com>
Cc: linux-block@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"open list:SOFTWARE RAID (Multiple Disks) SUPPORT"
<linux-raid@vger.kernel.org>,
qkrwngud825@gmail.com, FB Kernel Team <Kernel-team@fb.com>,
"v4.3+" <stable@vger.kernel.org>, Jens Axboe <axboe@fb.com>,
Neil Brown <neilb@suse.de>
Subject: Re: [PATCH] MD: make bio mergeable
Date: Tue, 26 Apr 2016 08:21:21 -0600 [thread overview]
Message-ID: <571F7961.4090703@kernel.dk> (raw)
In-Reply-To: <CACVXFVMgKQmtKRQvkpyD5GMh0AN0i7uNyq8ecVvQQ5kmdLEm+A@mail.gmail.com>
On 04/26/2016 03:56 AM, Ming Lei wrote:
> On Tue, Apr 26, 2016 at 7:52 AM, Shaohua Li <shli@fb.com> wrote:
>> blk_queue_split marks bio unmergeable, which makes sense for normal bio.
>> But if dispatching the bio to underlayer disk, the blk_queue_split
>> checks are invalid, hence it's possible the bio becomes mergeable.
>
> If the bio from md is splitted and marked as NOMERGE, it means some
> queue limits are reached. So looks the raid's queue limit is set as not
> big enough, could your find which limit causes the splitting and nomerge?
raid0 sets a limit of the stripe size for IO. Once the IO has passed md,
there's no reason why we can't merge for the lower driver. This is
(potentially) a huge performance issue on trim, since a lot of devices
are trim ops / sec limited rather than throughput limited.
--
Jens Axboe
next prev parent reply other threads:[~2016-04-26 14:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-25 23:52 [PATCH] MD: make bio mergeable Shaohua Li
2016-04-25 23:52 ` Shaohua Li
2016-04-26 0:59 ` Jens Axboe
2016-04-26 1:15 ` Jens Axboe
2016-04-26 9:56 ` Ming Lei
2016-04-26 14:21 ` Jens Axboe [this message]
2016-04-26 15:17 ` Ming Lei
2016-04-28 20:00 ` Holger Kiehl
2016-04-28 21:19 ` Shaohua Li
2016-04-28 21:19 ` Shaohua Li
2016-04-29 9:23 ` Holger Kiehl
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