Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754746Ab1FMBDf (ORCPT ); Sun, 12 Jun 2011 21:03:35 -0400 Received: from mga01.intel.com ([192.55.52.88]:56598 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754301Ab1FMBDb (ORCPT ); Sun, 12 Jun 2011 21:03:31 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.65,356,1304319600"; d="scan'208";a="15435715" Subject: Re: CFQ: async queue blocks the whole system From: Shaohua Li To: Vivek Goyal Cc: Tao Ma , "linux-kernel@vger.kernel.org" , Jens Axboe In-Reply-To: <20110610092031.GD4183@redhat.com> 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> Content-Type: text/plain; charset="UTF-8" Date: Mon, 13 Jun 2011 09:03:29 +0800 Message-ID: <1307927009.15392.102.camel@sli10-conroe> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1583 Lines: 34 On Fri, 2011-06-10 at 17:20 +0800, 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. Sure, I have no objection to avoid write starvation for a light write workload. We definitely should do something for such workload. Your patch is a good start. But for a heavy write workload (for example, Ma's test), CFQ never can completely avoid write starvation. In such workload, write queue has only slow progress to handle requests. Thanks, Shaohua -- 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/