From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chen Gong Subject: Re: [PATCH] ACPI: Read TSC upon resume Date: Mon, 18 Oct 2010 10:41:48 +0800 Message-ID: <4CBBB3EC.9000609@linux.intel.com> References: <1286406919-6236-1-git-send-email-snanda@chromium.org> <20101007181536.GA24811@suse.de> <201010072344.22166.rjw@sisk.pl> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mga02.intel.com ([134.134.136.20]:41380 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752321Ab0JRCly (ORCPT ); Sun, 17 Oct 2010 22:41:54 -0400 In-Reply-To: Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Koornstra, Reinoud" Cc: "Rafael J. Wysocki" , Greg KH , Sameer Nanda , "lenb@kernel.org" , "stefan.bader@canonical.com" , "brad.figg@canonical.com" , "apw@canonical.com" , "linux-acpi@vger.kernel.org" , "linux-kernel@vger.kernel.org" =E4=BA=8E 10/16/2010 11:03 AM, Koornstra, Reinoud =E5=86=99=E9=81=93: >> -----Original Message----- >> From: linux-acpi-owner@vger.kernel.org [mailto:linux-acpi- >> owner@vger.kernel.org] On Behalf Of Rafael J. Wysocki >> Sent: Thursday, October 07, 2010 2:44 PM >> To: Greg KH >> Cc: Sameer Nanda; lenb@kernel.org; stefan.bader@canonical.com; >> brad.figg@canonical.com; apw@canonical.com; linux-acpi@vger.kernel.o= rg; >> linux-kernel@vger.kernel.org >> Subject: Re: [PATCH] ACPI: Read TSC upon resume >> >> On Thursday, October 07, 2010, Greg KH wrote: >>> On Thu, Oct 07, 2010 at 11:05:21AM -0700, Sameer Nanda wrote: >>>> On Thu, Oct 7, 2010 at 10:46 AM, Greg KH wrote: >>>>> On Thu, Oct 07, 2010 at 10:43:34AM -0700, Sameer Nanda wrote: >>>>>> On Wed, Oct 6, 2010 at 7:19 PM, Greg KH wrote: >>>>>>> And are you always going to be printing this out? Why do we >> want to >>>>>>> know this every time? >>>>>>> >>>>>> >>>>>> Yes, every time. This helps track variance in BIOS resume times >> within a >>>>>> single boot. >>>>> >>>>> Is that really something that users can do something about? >>>> >>>> Aside from complaining to the BIOS vendors, no :) >>> >>> Then I would not recommend adding this patch, as it is irrelevant f= or >>> 99.9999% of all Linux users. >> >> It may be somewhat useful, but the rdtscll() call seems to be x86- >> specific, in >> which case it shouldn't be used at this place. > > Also, in the case of an intel core 2 duo cpu, the tsc is not stable, = hence upon resume the cpu is spinning up and the first tsc's will be sl= ower. > During idle-time the tsc will not be incremented. The tsc is only sta= bly incremented upon 100% cpu usage. It also doesn't increment faster i= n turbo mode in case of some core 2 duo and certainly the Nehalem cpu's= =2E Calculating in time in terms of tsc might not be so reliable. > If I'm wrong, please feel free to fix me. I have 2 questions to your answer: 1. CPU has a flag named constant_tsc to keep TSC always working in a=20 constant way, so it is irrelvant to the CPU freq. whether in turbo mode= =20 or any P-state CPU currently belongs to, TSC should be not affected.=20 IIRC, this flag should exist long before, at least before Core 2 duo. I= f=20 so, TSC shoule be stable in this kind of environment. 2. though during idle-time TSC will not be incremented, here I want to remind it is right before Westmere (TSC not always running), and you=20 mentioned "upon resume the cpu is spinning up and the first tsc's will=20 be slower", I don't know if this commit cd7240c0b can fix it up. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html