Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754537Ab0DTLF2 (ORCPT ); Tue, 20 Apr 2010 07:05:28 -0400 Received: from casper.infradead.org ([85.118.1.10]:52392 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754507Ab0DTLF1 (ORCPT ); Tue, 20 Apr 2010 07:05:27 -0400 Date: Tue, 20 Apr 2010 04:07:08 -0700 From: Arjan van de Ven To: Thomas Renninger Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mingo@elte.hu, peterz@infradead.org, tglx@linutronix.de, davej@redhat.com, cpufreq@vger.kernel.org Subject: Re: [PATCH 7/7] ondemand: Solve the big performance issue with ondemand during disk IO Message-ID: <20100420040708.1ae390b1@infradead.org> In-Reply-To: <201004201129.02370.trenn@suse.de> References: <20100418115949.7b743898@infradead.org> <20100418120346.1b478410@infradead.org> <201004201129.02370.trenn@suse.de> Organization: Intel X-Mailer: Claws Mail 3.7.5 (GTK+ 2.16.6; i586-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1283 Lines: 31 On Tue, 20 Apr 2010 11:29:02 +0200 Thomas Renninger wrote: > Have you looked at: > /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_transition_latency > and > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/sampling_rate > Transition latency comes from ACPI tables and sampling rate depends > on it. of course I have; in practice on systems i use it is always a 10 milliseconds interval, which is the minimum it gets. Yes this was a bug, no it wasn't the bug here ;-) > Reducing the sampling rate, significantly reduces performance loss while it does, it is not nearly sufficient for the alternating IO/CPU cases I've looked at. I've looked at many timecharts for various IO/CPU workloads, including my normal own use as well as Andrews and the CPU busy periods are in the 1 - 20 msec range between IOs most of the time, for which a 10 msec sampling is obviously problematic. -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org -- 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/