From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Subject: Re: [PATCH] aio: optimize free kioctx slot search Date: Fri, 27 Dec 2013 05:32:50 -0700 Message-ID: <20131227123250.GA22587@parisc-linux.org> References: <52BC0352.2040504@cn.fujitsu.com> <20131226141356.GH11091@parisc-linux.org> <52BD5738.4010308@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Benjamin , linux-aio@kvack.org, fsdevel , linux-kernel To: Gu Zheng Return-path: Received: from palinux.external.hp.com ([192.25.206.14]:36738 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751307Ab3L0Mcx (ORCPT ); Fri, 27 Dec 2013 07:32:53 -0500 Content-Disposition: inline In-Reply-To: <52BD5738.4010308@cn.fujitsu.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Fri, Dec 27, 2013 at 06:32:24PM +0800, Gu Zheng wrote: > Hi Matthew, > On 12/26/2013 10:13 PM, Matthew Wilcox wrote: > > > On Thu, Dec 26, 2013 at 06:22:10PM +0800, Gu Zheng wrote: > >> to the new free slot if it's smaller than 'next_free'. So that we can > >> ensure that the slots before 'next_free' are all used, and the search can start > >> from 'next_free' to reduce the search and improve the performance. > > > > Have you benchmarked it? What kinds of improvements are you seeing? > > Not yet. But the improvement is obvious, we can always reduce the search region and > improve the hit rate when trying to find a free slot with this change. It's not so obvious to me. You've added extra stores, which may dirty an additional cacheline. That may end up costing more than it saves. I suspect the difference is lost in the noise, but I've been wrong about these things before. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step."