From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stan Hoeppner Subject: Re: [patch 0/3 v3] MD: improve raid1/10 write performance for fast storage Date: Thu, 28 Jun 2012 20:29:21 -0500 Message-ID: <4FED04F1.8010902@hardwarefreak.com> References: <20120613091143.508417333@kernel.org> <20120628190352.4dc1dd76@notabene.brown> Reply-To: stan@hardwarefreak.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120628190352.4dc1dd76@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: Shaohua Li , linux-raid@vger.kernel.org, axboe@kernel.dk List-Id: linux-raid.ids On 6/28/2012 4:03 AM, NeilBrown wrote: > On Wed, 13 Jun 2012 17:11:43 +0800 Shaohua Li 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