Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757454Ab1BKAga (ORCPT ); Thu, 10 Feb 2011 19:36:30 -0500 Received: from smtp-out.google.com ([216.239.44.51]:9789 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752822Ab1BKAg2 convert rfc822-to-8bit (ORCPT ); Thu, 10 Feb 2011 19:36:28 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=l2xAdJBjbeB1ZJGYjt55jnbaxkq6Zs6mAY56uUGPUp3twfi5FQsJFCw8r+pgqC201a bZdA2wn/EvPPX7od4BPA== MIME-Version: 1.0 In-Reply-To: References: <20110210013211.21573.69260.stgit@neat.mtv.corp.google.com> <20110210020946.GA27040@redhat.com> <20110210035738.GC27040@redhat.com> Date: Thu, 10 Feb 2011 16:36:25 -0800 Message-ID: Subject: Re: [PATCH] Avoid preferential treatment of groups that aren't backlogged From: Chad Talbott To: Vivek Goyal Cc: jaxboe@fusionio.com, guijianfeng@cn.fujitsu.com, mrubin@google.com, teravest@google.com, jmoyer@redhat.com, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2141 Lines: 48 On Thu, Feb 10, 2011 at 10:57 AM, Chad Talbott wrote: > On Wed, Feb 9, 2011 at 7:57 PM, Vivek Goyal wrote: >> If you ran different random readers in different groups of differnet >> weight with group_isolation=1, then there is a case of having service >> differentiation. In that case we will idle for 8ms on each group before >> we expire the group. So in these test cases are low weight groups not >> submitting IO with-in 8ms? Putting a random reader in separate group >> with think time > 8, I think is going to hurt a lot because for every >> single IO dispatched group is going to weight for 8ms before it is >> expired. > > You're right about the behavior of group_idle. ?We have more > experience with earlier kernels (before group_idle). ?With this patch > we are able to achieve isolation without group_idle even with these > large ratios. ?(Without group_idle the random reader workloads will > get marked seeky, and idling is disabled. ?Without group_idle, we have > to remember the vdisktime to get isolation.) > >> Can you run blktrace and verify what's happenig? > > I can run a blktrace, and I think it will show what you expect. So, I ran the following two tests and took a blktrace. 950 rdrand, 50 rdrand.delay10 weight 950 random reader with low think time vs weight 50 random reader with 10ms think time 950 rdrand, 50 rdrand.delay50 # 50ms think time weight 950 random reader with low think time vs weight 50 random reader with 50ms think time I find that we are still idling for these random readers, even the one with 50ms think time. group_idle is 0 according to blktrace. With this patch, both of these cases have correct isolation. Without this patch, the small weight reader is able to get more than its share. I think that idling for a random reader with a 50ms think time is likely a bug, but a separate issue. Chad -- 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/