From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Subject: Re: [PATCH] qla2xxx: Resolved a performance issue in interrupt Date: Wed, 10 Jun 2009 13:48:11 -0600 Message-ID: <20090610194810.GU3274@parisc-linux.org> References: <20080911201140.GM2772@parisc-linux.org> <20090610183259.GI89096@n6013ncj7y1lh1.qlogic.org> <1244661018.17432.21.camel@mulgrave.site> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from palinux.external.hp.com ([192.25.206.14]:52885 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761316AbZFJTsK (ORCPT ); Wed, 10 Jun 2009 15:48:10 -0400 Content-Disposition: inline In-Reply-To: <1244661018.17432.21.camel@mulgrave.site> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: Andrew Vasquez , "Wilcox, Matthew R" , Anirban Chakraborty , David Wagner , Linux SCSI Mailing List , douglas.w.styner@intel.com, sharad.c.tripathi@intel.com, chinang.ma@intel.com, terry.o.prickett@intel.com On Wed, Jun 10, 2009 at 07:10:18PM +0000, James Bottomley wrote: > > That's a curious observation... I'm just trying to understand the > > numbers here, but, are we sure that this spin_lock() -> > > spin_lock_irqsave() conversion is in fact the mitigating factor. > > I think so ... the performance of both fixes is actually nearly > identical showing that the base reason (interrupt while holding hardware > spinlock adding to latency) is the correct one. > > The curiosity I had is whether we can do even better by disabling > interrupts for the whole of the ISR rather than only over the sections > where we take the hw lock, and I don't think we have conclusive evidence > either way on that. It probably doesn't matter much either way. At some point, I think Peter will be successful in forcing IRQF_DISABLED for all interrupts, and this decision will go away. -- 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."