From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754700Ab2AaOrs (ORCPT ); Tue, 31 Jan 2012 09:47:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:11825 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753280Ab2AaOrr (ORCPT ); Tue, 31 Jan 2012 09:47:47 -0500 Date: Tue, 31 Jan 2012 09:47:34 -0500 From: Vivek Goyal To: Shaohua Li Cc: lkml , linux-mm , Andrew Morton , Jens Axboe , Herbert Poetzl , Eric Dumazet , Wu Fengguang Subject: Re: [PATCH] fix readahead pipeline break caused by block plug Message-ID: <20120131144734.GA4378@redhat.com> References: <1327996780.21268.42.camel@sli10-conroe> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1327996780.21268.42.camel@sli10-conroe> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 31, 2012 at 03:59:40PM +0800, Shaohua Li wrote: > Herbert Poetzl reported a performance regression since 2.6.39. The test > is a simple dd read, but with big block size. The reason is: > > T1: ra (A, A+128k), (A+128k, A+256k) > T2: lock_page for page A, submit the 256k > T3: hit page A+128K, ra (A+256k, A+384). the range isn't submitted > because of plug and there isn't any lock_page till we hit page A+256k > because all pages from A to A+256k is in memory > T4: hit page A+256k, ra (A+384, A+ 512). Because of plug, the range isn't > submitted again. Why IO is not submitted because of plug? Doesn't task now get scheduled out causing an unplug? IOW, are we now busy waiting somewhere preventing unplug? Thanks Vivek