Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261577AbVDTMLO (ORCPT ); Wed, 20 Apr 2005 08:11:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261573AbVDTMLN (ORCPT ); Wed, 20 Apr 2005 08:11:13 -0400 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:16516 "EHLO amd.ucw.cz") by vger.kernel.org with ESMTP id S261546AbVDTMJO (ORCPT ); Wed, 20 Apr 2005 08:09:14 -0400 Date: Wed, 20 Apr 2005 14:08:46 +0200 From: Pavel Machek To: Dominik Brodowski , Thomas Renninger , Tony Lindgren , Frank Sorenson , linux-kernel@vger.kernel.org, Benjamin Herrenschmidt , Arjan van de Ven , Martin Schwidefsky , Andrea Arcangeli , George Anzinger , Thomas Gleixner , john stultz , Zwane Mwaikambo , Lee Revell , ML ACPI-devel , Bodo Bauer , Andi Kleen Subject: Re: [PATCH] Updated: Dynamic Tick version 050408-1 - C-state measures Message-ID: <20050420120846.GA21897@elf.ucw.cz> References: <20050408075001.GC4477@atomide.com> <42564584.4080606@tuxrocks.com> <42566C22.4040509@suse.de> <20050408115535.GI4477@atomide.com> <42651C38.6090807@suse.de> <20050419152723.GA9509@isilmar.linta.de> <42657222.5080601@suse.de> <20050420114433.GA28362@isilmar.linta.de> <20050420115739.GB16819@elf.ucw.cz> <20050420120102.GB28491@isilmar.linta.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050420120102.GB28491@isilmar.linta.de> X-Warning: Reading this can be dangerous to your mental health. User-Agent: Mutt/1.5.6+20040907i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1830 Lines: 42 Hi! > > > > Because I don't consider whether there was bm_activity the last ms, I only > > > > consider the average, it seems to happen that I try to trigger > > > > C3/C4 when there is just something copied and some bm active ?!? > > > > > > I don't think that this is perfect behaviour: if the system is idle, and > > > there is _currently_ bus master activity, the CPU should be put into C1 or > > > C2 type sleep. If you select C3 and actually enter it, you're risking > > > DMA issues, AFAICS. > > > > What kinds of DMA issues? Waiting 32msec or so is only heuristic; it > > can go wrong any time. It would be really bad if it corrupted data or > > something like that. > > loop() > a) bus mastering activity is going on at the very moment > b) the CPU is entering C3 > c) the CPU is woken out of C3 because of bus mastering activity > > the repeated delay between b) and c) might be problematic, as can be seen > by the comment in processor_idle.c: > > * TBD: A better policy might be to fallback to the demotion > * state (use it for this quantum only) istead of > * demoting -- and rely on duration as our sole demotion > * qualification. This may, however, introduce DMA > * issues (e.g. floppy DMA transfer overrun/underrun). > */ > > I'm not so worried about floppy DMA but about the ipw2x00 issues here. Like "ipw2x00 looses packets" if this happens too often? Pavel -- Boycott Kodak -- for their patent abuse against Java. - 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/