From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: trying to understand READ_META, READ_SYNC, WRITE_SYNC & co Date: Wed, 23 Jun 2010 12:02:52 +0200 Message-ID: <20100623100252.GB9575@lst.de> References: <20100621094828.GA30748@lst.de> <4C1F3916.4070608@kernel.dk> <20100621202504.GA6474@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jens Axboe , Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Vivek Goyal Return-path: Content-Disposition: inline In-Reply-To: <20100621202504.GA6474@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Mon, Jun 21, 2010 at 04:25:04PM -0400, Vivek Goyal wrote: > In my testing in the past, this was helping if lots of sequential readers > are running in a system (with 100ms slice each) and if there is another > reader doing small file reads. Without meta data based preemption check, > latency of opening small file used to be very high (Because all the sync > sequntial reader gets to consume their 100ms slices first). > > Situation should be somewhat better now after corrado's changes of > reducing slice length dynamically. But I suspect that we will still > experience significantly reduced latency for small file reads in presece > of multiple sequntial reads going on. Any chance we could create a benchmark suite for the I/O schedulers? I'd really like to get these annotations correct, and having an automated suite that shows the numbers for the interesting workloads would help greatly with that.