From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751569Ab1AWK31 (ORCPT ); Sun, 23 Jan 2011 05:29:27 -0500 Received: from mail-fx0-f46.google.com ([209.85.161.46]:55308 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751374Ab1AWK3Z (ORCPT ); Sun, 23 Jan 2011 05:29:25 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=Ua2ECvDOQQ7CpEUbYIKUt680CXCag8uugGe+9ldgwtpPX4qOcIHi1M/wiVTAbaB2T0 FzU3p48UT+h9PP4JbGDOxK84ma9i294KbzRrZ3FjzIxfh2FhHrev7hWqendzU+voohHm FuwAx7M1RpDWQq5zeoeggnz8enIYQUKv1jvmc= Date: Sun, 23 Jan 2011 11:29:20 +0100 From: Tejun Heo To: Vivek Goyal Cc: axboe@kernel.dk, tytso@mit.edu, djwong@us.ibm.com, shli@kernel.org, neilb@suse.de, adilger.kernel@dilger.ca, jack@suse.cz, snitzer@redhat.com, linux-kernel@vger.kernel.org, kmannth@us.ibm.com, cmm@us.ibm.com, linux-ext4@vger.kernel.org, rwheeler@redhat.com, hch@lst.de, josef@redhat.com Subject: Re: [PATCH 3/3] block: reimplement FLUSH/FUA to support merge Message-ID: <20110123102920.GB23121@htj.dyndns.org> References: <1295625598-15203-1-git-send-email-tj@kernel.org> <1295625598-15203-4-git-send-email-tj@kernel.org> <20110121185617.GI12072@redhat.com> <20110123102526.GA23121@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110123102526.GA23121@htj.dyndns.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jan 23, 2011 at 11:25:26AM +0100, Tejun Heo wrote: > Again, issuing flushes as fast as possible isn't necessarily better. > It might feel counter-intuitive but it generally makes sense to delay > flush if there are a lot of concurrent flush activities going on. > Another related interesting point is that with flush merging, > depending on workload, there's a likelihood that FUA, even if the > device supports it, might result in worse performance than merged DATA > + single POSTFLUSH sequence. Let me add a bit. In general, I'm a bit skeptical about the usefulness of hardware FUA on a rotating disk. All it saves is a single command issue overhead. On storage array or SSDs, the balance might be different tho. Event hen, with flush merging, I think it would heavily depend on the workload which way it would turn out. Thanks. -- tejun