From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932159Ab2IQP1h (ORCPT ); Mon, 17 Sep 2012 11:27:37 -0400 Received: from mga01.intel.com ([192.55.52.88]:60790 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932093Ab2IQP1g (ORCPT ); Mon, 17 Sep 2012 11:27:36 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.80,437,1344236400"; d="scan'208";a="223056392" Date: Mon, 17 Sep 2012 23:30:20 -0400 From: Youquan Song To: Daniel Lezcano Cc: Youquan Song , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, arjan@linux.intel.com, lenb@kernel.org, Rik van Riel , Youquan Song Subject: Re: [PATCH V2 0/3] x86,idle: Enhance cpuidle prediction to handle its failure Message-ID: <20120918033020.GA20862@linux-youquan.bj.intel.com> References: <1347933209-25939-1-git-send-email-youquan.song@intel.com> <50573934.4030102@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50573934.4030102@linaro.org> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > One case is turbostat utility (tools/power/x86/turbostat) at kernel 3.3 or early > > . turbostat utility will read 10 registers one by one at Sandybridge, so it will > > generate 10 IPIs to wake up idle CPUs. So cpuidle menu governor will predict it > > is repeat mode and there is another IPI wake up idle CPU soon, so it keeps idle > > CPU stay at C1 state even though CPU is totally idle. However, in the turbostat > > , following 10 registers reading is sleep 5 seconds by default, so the idle CPU > > will keep at C1 for a long time though it is idle until break event occurs. > > In a idle Sandybridge system, run "./turbostat -v", we will notice that deep > > C-state dangles between "70% ~ 99%". After patched the kernel, we will notice > > deep C-state stays at >99.98%. > > Is there an impact on performances ? In this case, turbostat is utility to measure cpu idle status and itself also is a workload to system. Its purpose is that show cpu C-state information every 5 seconds. After patched the kernel, it also does the same thing as usual. So I think the performance has no/little impact. I do not find performance impact in my tests. If you performance impact cases or suggestions, I will be very glad to try. Thanks -Youquan