Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754223Ab1FJJWA (ORCPT ); Fri, 10 Jun 2011 05:22:00 -0400 Received: from 0122700014.0.fullrate.dk ([95.166.99.235]:54807 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753405Ab1FJJV6 (ORCPT ); Fri, 10 Jun 2011 05:21:58 -0400 Message-ID: <4DF1E235.8010104@kernel.dk> Date: Fri, 10 Jun 2011 11:21:57 +0200 From: Jens Axboe MIME-Version: 1.0 To: Vivek Goyal CC: Tao Ma , Shaohua Li , linux-kernel@vger.kernel.org Subject: Re: CFQ: async queue blocks the whole system References: <1307616577-6101-1-git-send-email-tm@tao.ma> <20110609141451.GD29913@redhat.com> <4DF0DD0F.8090407@tao.ma> <20110609153738.GF29913@redhat.com> <4DF17C38.2010306@tao.ma> <4DF18933.4070904@tao.ma> <20110610092031.GD4183@redhat.com> In-Reply-To: <20110610092031.GD4183@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1435 Lines: 34 On 2011-06-10 11:20, Vivek Goyal wrote: > On Fri, Jun 10, 2011 at 11:02:11AM +0800, Tao Ma wrote: > > [..] >>> I don't think we can give a deadline for async request, because we >>> still want to give sync high priority. We can give async some slices, >>> so for a workload of small number of async requests and large number >>> sync requests, we don't starve async too much. But for a workload with >>> large number of sync/async requests, async will be starved for sure >>> and we can't solve this in cfq. >> OK, so if you guys thinks a 500 seconds wait is good for an async write >> to complete, fine, then we have to switch to deadline. > > I don't think that starving WRITES completely is a good idea. Especially > given the fact that you were not able to dispatch WRITES for 500 seconds. > This needs fixing. > > Its not about giving hard deadline to WRITES, but making sure we don't > starve them completely and they also make some progress. Agree, we need to have some sort of forward progress guarantee at least. Starving buffered writes indefinitely is surely a BUG. And it must be a regression from not that long ago. Trying to catch up with this thread... -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/