Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262116AbUKVNpS (ORCPT ); Mon, 22 Nov 2004 08:45:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262099AbUKVNnz (ORCPT ); Mon, 22 Nov 2004 08:43:55 -0500 Received: from mx1.elte.hu ([157.181.1.137]:17068 "EHLO mx1.elte.hu") by vger.kernel.org with ESMTP id S262103AbUKVNk7 (ORCPT ); Mon, 22 Nov 2004 08:40:59 -0500 Date: Mon, 22 Nov 2004 15:42:48 +0100 From: Ingo Molnar To: Eran Mann Cc: linux-kernel@vger.kernel.org Subject: Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.30-2 Message-ID: <20041122144248.GB28211@elte.hu> References: <20041116125402.GA9258@elte.hu> <20041116130946.GA11053@elte.hu> <20041116134027.GA13360@elte.hu> <20041117124234.GA25956@elte.hu> <20041118123521.GA29091@elte.hu> <20041118164612.GA17040@elte.hu> <20041122005411.GA19363@elte.hu> <41A1A6E6.5090807@mrv.com> <20041122100140.GD6817@elte.hu> <41A1EAE0.9080504@mrv.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <41A1EAE0.9080504@mrv.com> User-Agent: Mutt/1.4.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1261 Lines: 31 * Eran Mann wrote: > >>I?m seeing latencies of up to ~2000 microseconds. see attached traces > >>file for a small sample. I think I?m missing something obvious > >>config-wise but I don?t know what... > ... > > >this seems to imply IDE DMA related hardware overhead. Apparently what > >happens is that with certain motherboards/chipsets, if IDE DMA happens > >then that DMA transfer _completely locks up_ the system bus. Nothing > >happens, and the CPU is stalled in essence until the end of the DMA > >request. > Right on. > After hdparm -d0 I see maximum latency of 35 us after a full kernel > build with a few GUI apps in the background. I?ll try to find a > reasonable compromise. it might make sense to report this to the hw vendor as well, as these latencies dont occur at _every_ IDE DMA, it might be some sort of chipset (or BIOS) bug they might want to see resolved as well (if this isnt a ship-and-forget vendor). 2 msec stalls are not nice to a fair number of applications. Ingo - 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/