Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752120AbaJAPWd (ORCPT ); Wed, 1 Oct 2014 11:22:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56781 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751822AbaJAPWb (ORCPT ); Wed, 1 Oct 2014 11:22:31 -0400 Date: Wed, 1 Oct 2014 16:31:15 +0100 From: Alexander Gordeev To: Tejun Heo Cc: linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org Subject: Re: [PATCH RESEND v3 5/6] AHCI: Optimize single IRQ interrupt processing Message-ID: <20141001153114.GE8971@agordeev.usersys.redhat.com> References: <20140923205710.GB17332@mtj.dyndns.org> <20140924104213.GA2695@agordeev.usersys.redhat.com> <20140924130444.GA16555@htj.dyndns.org> <20140924140844.GB2695@agordeev.usersys.redhat.com> <20140924143913.GH16555@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140924143913.GH16555@htj.dyndns.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 24, 2014 at 10:39:13AM -0400, Tejun Heo wrote: > Hello, Alexander. > > On Wed, Sep 24, 2014 at 03:08:44PM +0100, Alexander Gordeev wrote: > > > Hmmm, how would the whole system benefit from it if there's only > > > single device? Each individual servicing of the interrupt does more > > > now which includes scheduling which may end up adding to completion > > > latency. > > > > As Chuck noticed, non-AHCI hardware context handlers will benefit. > > Maybe I'm off but I'm kinda skeptical that we'd be gaining back the > overhead we pay by punting to a thread. Hi Tejun, As odd as it sounds, I did not mention there is *no* change in IO performance at all (in my system): neither with one drive nor two. The change is only about how the interrupt handlers co-exist with other devices. I am attaching excerpts from some new perf tests I have done (this time in legacy interrupt mode). As you can notice, ahci_interrupt() CPU time drops from 4% to none. As of your concern wrt threaded handler invocation overhead - I am not quite sure here, but if SCHED_FIFO policy (the handler runs with) makes the difference? Anyway, as said above the overall IO does not suffer. > -- > tejun -- Regards, Alexander Gordeev agordeev@redhat.com -- 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/