Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752235Ab0HPCJQ (ORCPT ); Sun, 15 Aug 2010 22:09:16 -0400 Received: from TYO201.gate.nec.co.jp ([202.32.8.193]:44553 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751915Ab0HPCJP (ORCPT ); Sun, 15 Aug 2010 22:09:15 -0400 Date: Mon, 16 Aug 2010 11:07:37 +0900 From: Naoya Horiguchi To: Jeff Moyer Cc: Christoph Lameter , Andi Kleen , Andrew Morton , Mel Gorman , Wu Fengguang , "Jun'ichi Nomura" , linux-mm , LKML , Andrea Arcangeli Subject: Re: [RFC] [PATCH 2/4] dio: add page locking for direct I/O Message-ID: <20100816020737.GA19531@spritzera.linux.bs1.fc.nec.co.jp> References: <1281432464-14833-1-git-send-email-n-horiguchi@ah.jp.nec.com> <20100812075323.GA6112@spritzera.linux.bs1.fc.nec.co.jp> <20100812075941.GD6112@spritzera.linux.bs1.fc.nec.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-2022-jp Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2234 Lines: 43 Hi, On Thu, Aug 12, 2010 at 09:42:21AM -0400, Jeff Moyer wrote: > Naoya Horiguchi writes: > > > Basically it is user's responsibility to take care of race condition > > related to direct I/O, but some events which are out of user's control > > (such as memory failure) can happen at any time. So we need to lock and > > set/clear PG_writeback flags in dierct I/O code to protect from data loss. > > Did you do any performance testing of this? If not, please do and > report back. I'm betting users won't be pleased with the results. Here is the result of my direct I/O benchmarck, which mesures the time it takes to do direct I/O for 20000 pages on 2MB buffer for four types of I/O. Each I/O is issued for one page unit and each number below is the average of 25 runs. with patchset 2.6.35-rc3 Buffer I/O type average(s) STD(s) average(s) STD(s) diff(s) hugepage Sequential Read 3.87 0.16 3.88 0.20 -0.01 Sequential Write 7.69 0.43 7.69 0.43 0.00 Random Read 5.93 1.58 6.49 1.45 -0.55 Random Write 13.50 0.28 13.41 0.30 0.09 anonymous Sequential Read 3.88 0.21 3.89 0.23 -0.01 Sequential Write 7.86 0.39 7.80 0.34 0.05 Random Read 7.67 1.60 6.86 1.27 0.80 Random Write 13.50 0.25 13.52 0.31 -0.01 >From this result, although fluctuation is relatively large for random read, differences between vanilla kernel and patched one are within the deviations and it seems that adding direct I/O lock makes little or no impact on performance. And I know the workload of this benchmark can be too simple, so please let me know if you think we have another workload to be looked into. Thanks, Naoya Horiguchi -- 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/