From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757335Ab0HQQsd (ORCPT ); Tue, 17 Aug 2010 12:48:33 -0400 Received: from smtp-outbound-1.vmware.com ([65.115.85.69]:25755 "EHLO smtp-outbound-1.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753129Ab0HQQsa (ORCPT ); Tue, 17 Aug 2010 12:48:30 -0400 Subject: Re: [Patch] Skip cpu_calibrate for kernel running under hypervisors. From: Alok Kataria Reply-To: akataria@vmware.com To: "H. Peter Anvin" Cc: the arch/x86 maintainers , Greg KH , "greg@kroah.com" , "ksrinivasan@novell.com" , LKML In-Reply-To: <4C6A2C98.4060605@zytor.com> References: <1281986754.23253.32.camel@ank32.eng.vmware.com> <4C69D02F.6090601@zytor.com> <1282024311.20786.2.camel@ank32.eng.vmware.com> <4C6A2C98.4060605@zytor.com> Content-Type: text/plain Organization: VMware INC. Date: Tue, 17 Aug 2010 09:48:30 -0700 Message-Id: <1282063710.4388.11.camel@ank32.eng.vmware.com> Mime-Version: 1.0 X-Mailer: Evolution 2.12.3 (2.12.3-8.el5_2.3) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi HPA, On Mon, 2010-08-16 at 23:30 -0700, H. Peter Anvin wrote: > On 08/16/2010 10:51 PM, Alok Kataria wrote: > >> > >> I'm somewhat reluctant to take this one, since it assumes all the > >> hypervisors act the same. This seems rather inherently wrong. In fact, > >> the whole statement is fishy as heck... instead of being dependent on > >> AMD and so on, > > > > The check about being on AMD is something that was already there. > > > > I know it was... and calibrate_cpu() seems to be an AMD-specific > function, but that's rather crappy. I'm thinking that perhaps we should > make it an x86_init function, then the AMD CPU detection can install it > and the vmware hypervisor detection can uninstall it. I am planning to add a calibrate_apic function ptr in x86_platform_ops, for getting the APIC frequency too directly from the hypervisor. If you want I can add this calibrate_cpu function ptr too or is the patch below okay for now ? Thanks, Alok > > >> this should either be a function pointer or a CPU > >> (mis)feature bit. > > > > In any case, I agree that my previous patch did assume all hypervisors > > to be same, which might be wrong. How about using the > > X86_FEATURE_TSC_RELIABLE bit for this too ? i.e. Skip cpu_calibrate call > > if TSC_RELIABLE bit is set. As of now that bit is set for vmware only. > > > > Something like the below. > > > > Signed-off-by: Alok N Kataria > > Cc: H. Peter Anvin > > > > Index: linux-x86-tree.git/arch/x86/kernel/tsc.c > > =================================================================== > > --- linux-x86-tree.git.orig/arch/x86/kernel/tsc.c 2010-08-03 12:21:20.000000000 -0700 > > +++ linux-x86-tree.git/arch/x86/kernel/tsc.c 2010-08-16 21:59:32.000000000 -0700 > > @@ -927,7 +927,8 @@ void __init tsc_init(void) > > } > > > > if (cpu_has(&boot_cpu_data, X86_FEATURE_CONSTANT_TSC) && > > - (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)) > > + (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) && > > + !(cpu_has(&boot_cpu_data, X86_FEATURE_TSC_RELIABLE))) > > cpu_khz = calibrate_cpu(); > > > > printk("Detected %lu.%03lu MHz processor.\n", > > > > That seems like a much better approach. > > -hpa >