Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755271AbZCULOU (ORCPT ); Sat, 21 Mar 2009 07:14:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753150AbZCULOF (ORCPT ); Sat, 21 Mar 2009 07:14:05 -0400 Received: from brick.kernel.dk ([93.163.65.50]:34600 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753116AbZCULOC (ORCPT ); Sat, 21 Mar 2009 07:14:02 -0400 Date: Sat, 21 Mar 2009 12:14:00 +0100 From: Jens Axboe To: Andrew Morton Cc: Jerome Marchand , linux-kernel@vger.kernel.org Subject: Re: [PATCH] block: forbid to re-enable I/O stat accounting Message-ID: <20090321111400.GJ27476@kernel.dk> References: <200903201333.n2KDXONh023780@dhcp-0-152.brq.redhat.com> <20090321030309.f783ec8c.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090321030309.f783ec8c.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1403 Lines: 35 On Sat, Mar 21 2009, Andrew Morton wrote: > > Please fix your email headers - what I received was > > From: Jerome Marchand > To: unlisted-recipients:;;@imap1.linux-foundation.org (no To-header on input) > Cc: Jens Axboe Ditto, I didn't think anyone else got it. At least noone else got my reply :-) > On Thu, 19 Mar 2009 11:36:50 +0100 Jerome Marchand wrote: > > > When we stop I/O stat accounting we stop to update the in-flight > > requests counter and we need this counter to be reliable for > > accounting I/O stats. Unfortunately updating in_flight field may > > affect performance. So, until we have a better solution, just forbid > > to re-enable I/O stat accounting after it has been disabled. > > hm. Is it really so hard to just quiesce the device until all in-flight > requests have drained? freeze_bdev() might be a suitable starting point? That was my suggestion as well, we really need to be able to turn it back on again. Ideally, I'd like iostat and friends to turn it on/off when somebody does the monitoring. A one-way street option is not very nice. -- Jens Axboe -- 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/