From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757391AbaC0VwX (ORCPT ); Thu, 27 Mar 2014 17:52:23 -0400 Received: from mail-pa0-f44.google.com ([209.85.220.44]:60547 "EHLO mail-pa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757281AbaC0VwV (ORCPT ); Thu, 27 Mar 2014 17:52:21 -0400 Message-ID: <53349D92.1050907@linaro.org> Date: Thu, 27 Mar 2014 14:52:18 -0700 From: John Stultz User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Andy Lutomirski CC: Clemens Ladisch , Feng Tang , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Linux Kernel Mailing List , Dave Hansen Subject: Re: [PATCH] x86: hpet: Don't default CONFIG_HPET_TIMER to be y for X86_64 References: <1395906309-7519-1-git-send-email-feng.tang@intel.com> <53340561.4050708@ladisch.de> <53348199.7070207@mit.edu> In-Reply-To: X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/27/2014 02:33 PM, Andy Lutomirski wrote: > On Thu, Mar 27, 2014 at 2:27 PM, John Stultz wrote: >> On Thu, Mar 27, 2014 at 12:52 PM, Andy Lutomirski wrote: >>> On 03/27/2014 04:02 AM, Clemens Ladisch wrote: >>>> Feng Tang wrote: >>>> The help text still says: >>>> | You can safely choose Y here. [...] >>>> | Choose N to continue using the legacy 8254 timer. >>>> >>>> Are these statements still true for those platforms? >>> They aren't true for modern desktop and server platforms -- the TSC is >>> used regardless of hpet availability. >> While I suspect the comment above is in relation to the non-apic >> timer. But with respect to timekeeping, our point is true assuming the >> TSC isn't mucked up by the BIOS. My 1yr old i7-3930k single socket >> system still has some wonky BIOS bug that offsets the boot core's TSC. >> And that's intel's bios, so I can only imagine other vendors have >> found other ways to cause trouble. > Is this, perhaps, an MSI X79A-GD65 (8D) (MS-7760)? If so, there's a fixed BIOS. Actually, an Intel DX79TO. I've harangued some folks I know, but no fixes for the BIOS have been released. >> So yea, the hpet availability for timekeeping is still important, as >> the TSC can still be problematic. > Is HPET really that much better than acpi_pm? I can read my HPET in > ~584ns (vdso) or ~649ns (syscall) and my acpi_pm in 753ns. So it's > better, but not by a whole lot. I know on older hardware it was a bigger win. I'd have to look at what my current system does. > But yes, I see no good reason to disable it, except specifically on > systems where there are known bugs. Agreed. thanks -john