From: Stan Hoeppner <stan@hardwarefreak.com>
To: NeilBrown <neilb@suse.de>
Cc: Shaohua Li <shli@kernel.org>,
linux-raid@vger.kernel.org, axboe@kernel.dk
Subject: Re: [patch 0/3 v3] MD: improve raid1/10 write performance for fast storage
Date: Thu, 28 Jun 2012 20:29:21 -0500 [thread overview]
Message-ID: <4FED04F1.8010902@hardwarefreak.com> (raw)
In-Reply-To: <20120628190352.4dc1dd76@notabene.brown>
On 6/28/2012 4:03 AM, NeilBrown wrote:
> On Wed, 13 Jun 2012 17:11:43 +0800 Shaohua Li <shli@kernel.org> wrote:
>
>> In raid1/10, all write requests are dispatched in a single thread. In fast
>> storage, the thread is a bottleneck, because it dispatches request too slow.
>> Also the thread migrates freely, which makes request completion cpu not match
>> with submission cpu even driver/block layer has such capability. This will
>> cause bad cache issue. Both these are not a big deal for slow storage.
>>
>> Switching the dispatching to percpu/perthread based dramatically increases
>> performance. The more raid disk number is, the more performance boosts. In a
>> 4-disk raid10 setup, this can double the throughput.
>>
>> percpu/perthread based dispatch doesn't harm slow storage. This is the way how
>> raw device is accessed, and there is correct block plug set which can help do
>> request merge and reduce lock contention.
>>
>> V2->V3:
>> rebase to latest tree and fix cpuhotplug issue
>>
>> V1->V2:
>> 1. droped direct dispatch patches. That has better performance imporvement, but
>> is hopelessly made correct.
>> 2. Add a MD specific workqueue to do percpu dispatch.
> I still don't like the per-cpu allocations and the extra work queues.
Why don't you like this method Neil? Complexity? The performance seems
to be there.
--
Stan
next prev parent reply other threads:[~2012-06-29 1:29 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-13 9:11 [patch 0/3 v3] MD: improve raid1/10 write performance for fast storage Shaohua Li
2012-06-13 9:11 ` [patch 1/3 v3] MD: add a specific workqueue to do dispatch Shaohua Li
2012-06-13 9:11 ` [patch 2/3 v3] raid1: percpu dispatch for write request if bitmap supported Shaohua Li
2012-06-13 9:11 ` [patch 3/3 v3] raid10: " Shaohua Li
2012-06-28 9:03 ` [patch 0/3 v3] MD: improve raid1/10 write performance for fast storage NeilBrown
2012-06-29 1:29 ` Stan Hoeppner [this message]
2012-06-29 2:52 ` NeilBrown
2012-06-29 3:02 ` Roberto Spadim
2012-06-30 4:37 ` Stan Hoeppner
2012-06-29 6:10 ` Shaohua Li
2012-07-02 7:36 ` Shaohua Li
2012-07-03 8:58 ` Shaohua Li
2012-07-04 1:45 ` NeilBrown
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