Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756329AbZKMRTD (ORCPT ); Fri, 13 Nov 2009 12:19:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755972AbZKMRTA (ORCPT ); Fri, 13 Nov 2009 12:19:00 -0500 Received: from mail-iw0-f178.google.com ([209.85.223.178]:60766 "EHLO mail-iw0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755887AbZKMRS6 (ORCPT ); Fri, 13 Nov 2009 12:18:58 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; b=eVHsiSZEpnAOTKdBI6+vHpzP0smei921+6F3omdd6MH6OXUWHhUXBP6NE++pyZIiMb Go/vhXTadZO1bOi1NGWDVHuDbUXA7N/tACsmErmQKi1Qk/4/Qc98UD3iZ5XXZinINXlx D3/ECOaGrJGDheACR2l/Mza6vfamj95sk7J8c= MIME-Version: 1.0 In-Reply-To: <4e5e476b0911100412yb51d472r24be8b2068204348@mail.gmail.com> References: <1257537660-5301-1-git-send-email-lrodriguez@atheros.com> <200911072152.57596.trenn@suse.de> <4AF5F47C.5000402@linux.intel.com> <200911072347.05786.trenn@suse.de> <4AF5FBC7.9000105@linux.intel.com> <43e72e890911090832v1c809482yde7e767502271376@mail.gmail.com> <4e5e476b0911100412yb51d472r24be8b2068204348@mail.gmail.com> From: "Luis R. Rodriguez" Date: Fri, 13 Nov 2009 09:18:43 -0800 Message-ID: <43e72e890911130918v5a4c4fabt2deda5a4ab75ff5@mail.gmail.com> Subject: Re: [PATCH] cpu-freq: add troubleshooting section for FSB changes To: Corrado Zoccolo Cc: Arjan van de Ven , Senthil Balasubramanian , Aeolus Yang , Jonathan May , Thomas Renninger , davej@redhat.com, cpufreq@vger.kernel.org, linux-kernel@vger.kernel.org, Matthew Garrett , Reinette Chatre , Amod Bodas , David Quan , Kishore Jotwani , linux-wireless Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2311 Lines: 48 On Tue, Nov 10, 2009 at 4:12 AM, Corrado Zoccolo wrote: > Hi, > On Mon, Nov 9, 2009 at 5:32 PM, Luis R. Rodriguez wrote: >> >> And we tested this (reducing the min cpu freq to one less than the >> highest supported P state to avoid an FSB speed change) and it seems >> doing the steps described here did not fix the issue. But at least now >> if anyone else wants to verify this they can with some sort of >> documentaiton. >> >> So to confirm though -- we are seeing a huge performance depredation >> mainly on RX on an Intel Pine Trail platform with SpeedStep enabled on >> the BIOS. >> >> Let me get into the specifics in case anyone is able to help. The >> issue is with ath9k on RX and the CPU on C3 state requesting DMA over >> PCI-E. We typically would get about 110 Mbps with an AR9285 (single >> stream) but when SpeedStep is enabled it goes down to 25 Mbps. At the >> PCI-E level we are seeing huge latencies introduced when SpeedStep is >> used for DMA requests to the Intel root complex on the Intel Pine >> trail platform. Latencies are about 20-60 us. > > You mentioned speedstep and cpufreq, but the problem is with C3 state > and cpuidle (probably the BIOS mixes the two concepts, but we should > keep them separated). > C3 is not related to the core or FSB frequency, it is an idle state. > When in C3, the CPU is not ready to perform any operation, not just > slower, and depending on the CPU hw, it may take several us to wake up > (even 85us, on an Atom). > >> >> Is there a timeout threshold change that will cause the Intel chipset >> wait for some time after completion before going into a C3 state? Are >> there any other explanations for seeing such huge latencies on C3 >> state? > There is a patch from Arjan for the cpuidle menu governor, that may fix it. > http://linux.derkeiler.com/Mailing-Lists/Kernel/2009-09/msg05276.html > It is already present in 2.6.32. Thanks all for your feedback -- this was determined to be a BIOS bug :) Anyway, hope you do consider the patch for inclusion. Luis -- 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/