From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751557AbWCOWDJ (ORCPT ); Wed, 15 Mar 2006 17:03:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751656AbWCOWDJ (ORCPT ); Wed, 15 Mar 2006 17:03:09 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:60351 "EHLO mx3.mail.elte.hu") by vger.kernel.org with ESMTP id S1751557AbWCOWDI (ORCPT ); Wed, 15 Mar 2006 17:03:08 -0500 Date: Wed, 15 Mar 2006 23:00:47 +0100 From: Ingo Molnar To: Lee Revell Cc: "Bill Rugolsky Jr." , Andi Kleen , Jeff Garzik , Jason Baron , linux-kernel@vger.kernel.org, john stultz Subject: Re: libata/sata_nv latency on NVIDIA CK804 [was Re: AMD64 X2 lost ticks on PM timer] Message-ID: <20060315220046.GA20469@elte.hu> References: <200602280022.40769.darkray@ic3man.com> <4408BEB5.7000407@garzik.org> <20060303234330.GA14401@ti64.telemetry-investments.com> <200603040107.27639.ak@suse.de> <20060315213638.GA17817@ti64.telemetry-investments.com> <1142459152.1671.64.camel@mindpipe> <20060315215848.GB18241@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060315215848.GB18241@elte.hu> User-Agent: Mutt/1.4.2.1i X-ELTE-SpamScore: 0.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=AWL autolearn=no SpamAssassin version=3.0.3 0.0 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Ingo Molnar wrote: > in this particular case there's only very simple (and non-IO) > instructions in that codepath (no loops either), except for > ata_bmdma_status() which does IO ops: so i agree with you that the > most likely candidate for the delay is the readb() or the inb() in > ata_bdma_status(). > > I'm wondering which one of the two. inb()s are known to be horrible on > some systems - but i've never seen them take 16 milliseconds. If it's > the inb(), then that could also involve SMM mode and IO > emulation/bug-workaround BIOS hackery - which could indeed cause such > delays. [but i havent seen such a thing either.] > > the other option is that this is a random delay [e.g. DMA starvation] > hitting ata_bmdma_status() only by accident. (That looks a bit > unlikely though, given how related this codepath seems to the whole > problem area.) i'd exclude this option based on the second latency trace: that too shows a delay in ata_bmdma_status(). so my guess would be that this device doesnt do MMIO, and the PIO inb() causes some bad BIOS-based SMM handler/emulator to trigger, which takes 16.6 msecs. If indeed the device is not in MMIO mode, is there a way to force it into MMIO mode, to test this theory? Ingo