From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754797Ab1AaTYF (ORCPT ); Mon, 31 Jan 2011 14:24:05 -0500 Received: from 0122700014.0.fullrate.dk ([95.166.99.235]:48475 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751579Ab1AaTYD (ORCPT ); Mon, 31 Jan 2011 14:24:03 -0500 Message-ID: <4D470C50.6010701@kernel.dk> Date: Mon, 31 Jan 2011 20:24:00 +0100 From: Jens Axboe MIME-Version: 1.0 To: Jeff Moyer CC: Vivek Goyal , linux kernel mailing list Subject: Re: [PATCH] blkio-throttle: Avoid calling blkiocg_lookup_group() for root group References: <20110117215606.GI5624@redhat.com> <20110126185729.GD6713@redhat.com> In-Reply-To: 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 On 2011-01-31 20:20, Jeff Moyer wrote: > Vivek Goyal writes: > >> On Mon, Jan 17, 2011 at 04:56:06PM -0500, Vivek Goyal wrote: >>> o Jeff Moyer was doing some testing on a RAM backed disk and >>> blkiocg_lookup_group() showed up high overhead after memcpy(). Similarly >>> somebody else reported that blkiocg_lookup_group() is eating 6% extra >>> cpu. Though looking at the code I can't think why the overhead of >>> this function is so high. One thing is that it is called with very high >>> frequency (once for every IO). >>> >>> o For lot of folks blkio controller will be compiled in but they might >>> not have actually created cgroups. Hence optimize the case of root >>> cgroup where we can avoid calling blkiocg_lookup_group() if IO is happening >>> in root group (common case). >>> >>> Reported-by: Jeff Moyer >>> Signed-off-by: Vivek Goyal >> >> Hi Jens, >> >> Do you have any concerns regarding this patch? > > Acked-by: Jeff Moyer > > Jens, this is a pretty easy performance regression fixup. I think it > should be pulled in sooner rather than later. We've also witnessed this > slowdown on big performance testing rigs, so it's not just a ramdisk > issue. Yep, will fold it into 2.6.38, thanks! -- Jens Axboe