From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750868AbWHNHfr (ORCPT ); Mon, 14 Aug 2006 03:35:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750867AbWHNHfr (ORCPT ); Mon, 14 Aug 2006 03:35:47 -0400 Received: from brick.kernel.dk ([62.242.22.158]:47888 "EHLO kernel.dk") by vger.kernel.org with ESMTP id S1750743AbWHNHfq (ORCPT ); Mon, 14 Aug 2006 03:35:46 -0400 Date: Mon, 14 Aug 2006 09:37:25 +0200 From: Jens Axboe To: Andrew Morton Cc: David Miller , linux-kernel@vger.kernel.org Subject: Re: softirq considered harmful Message-ID: <20060814073724.GJ4231@suse.de> References: <20060812162857.d85632b9.akpm@osdl.org> <20060812.174324.77324010.davem@davemloft.net> <20060812174549.9a8f8aeb.akpm@osdl.org> <20060812.180944.51301787.davem@davemloft.net> <20060812182234.605b4fb4.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060812182234.605b4fb4.akpm@osdl.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 12 2006, Andrew Morton wrote: > On Sat, 12 Aug 2006 18:09:44 -0700 (PDT) > David Miller wrote: > > > From: Andrew Morton > > Date: Sat, 12 Aug 2006 17:45:49 -0700 > > > > > Is that also adding 150 usecs to each IO operation? > > > > I have no idea, Jens hasn't done enough to narrow down the true cause > > of the latencies he is seeing. So pinpointing it on anything specific > > is highly premature at this stage. > > Determining whether pre-conversion scsi was impacted in the same manner > would be part of that pinpointing process. > > Deferring to softirq _has_ to add latency and any latency addition in > synchronous disk IO is very bad. That being said, 150 usecs per request is > so bad that I'd be suspecting that it's not affecting most people, else > we'd have heard. Hopefully you often end up doing > 1 request for a busy IO sub system, otherwise the softirq stuff is pointless. But it's still pretty bad for single requests. > > My point was merely to encourage you to find out the facts before > > tossing accusations around. :-) > > No, your point was that slotting this change into mainline without telling > anyone was OK because SCSI has been doing something similar. Not similar, identical. Andrew, there was _no_ real change there! -- Jens Axboe