Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758449AbXKTERc (ORCPT ); Mon, 19 Nov 2007 23:17:32 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753665AbXKTERY (ORCPT ); Mon, 19 Nov 2007 23:17:24 -0500 Received: from smtp102.mail.mud.yahoo.com ([209.191.85.212]:24380 "HELO smtp102.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752541AbXKTERX (ORCPT ); Mon, 19 Nov 2007 23:17:23 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:X-YMail-OSG:From:To:Subject:Date:User-Agent:Cc:References:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding:Content-Disposition:Message-Id; b=qHy5mxTk1Y65XFTklEZFysG5k+tdBeDpNkUrnSg0/KN7Y4yalrIEC8qnVxfQ2bze/AA7RvgELo8KP1J5PjKVbgDnQ0gpB0ARIPj1ULI0CLBAHC2xwTy4+vRawqqUtO8PpBxQtLj0DpzwsRpSxlHHtbOF6Srk2yTYvRuw7JM9Ht4= ; X-YMail-OSG: wi8OAJIVM1mfMe.pcn7IuZ7B1jK.1iMZfUR0sChOV5JzDVkKSS5Coz46S_JnODwrOwCPFPuxbA-- From: Nick Piggin To: Mark Lord Subject: Re: CONFIG_IRQBALANCE for 64-bit x86 ? Date: Tue, 20 Nov 2007 15:17:15 +1100 User-Agent: KMail/1.9.5 Cc: Andrew Morton , Linus Torvalds , Ingo Molnar , Linux Kernel References: <47425EA5.7000607@rtr.ca> In-Reply-To: <47425EA5.7000607@rtr.ca> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200711201517.16171.nickpiggin@yahoo.com.au> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1558 Lines: 37 On Tuesday 20 November 2007 15:12, Mark Lord wrote: > On 32-bit x86, we have CONFIG_IRQBALANCE available, > but not on 64-bit x86. Why not? > > I ask, because this feature seems almost essential to obtaining > reasonable latencies during heavy I/O with fast devices. > > My 32-bit Core2Duo MythTV box drops audio frames without it, > but works perfectly *with* IRQBALANCE. > > My QuadCore box works very well in 32-bit mode with IRQBALANCE, > but responsiveness sucks bigtime when run in 64-bit mode (no IRQBALANCE) > during periods of multiple heavy I/O streams (USB flash drives). > > That's with both the 32 and 64 bit versions of Kubuntu Gutsy, > so the software uses pretty much identical versions either way. > > As near as I can tell, when IRQBALANCE is not configured, > all I/O device interrupts go to CPU#0. > > I don't think our CPU scheduler takes that into account when assigning > tasks to CPUs, so anything sent to CPU0 runs with very high latencies. > > Or something like that. > > Why no IRQ_BALANCE in 64-bit mode ? For that matter, I'd like to know why it has been decided that the best place for IRQ balancing is in userspace. It should be in kernel IMO, and it would probably allow better power saving, performance, fairness, etc. if it were to be integrated with the task balancer as well. - 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/