Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752475AbbFCA64 (ORCPT ); Tue, 2 Jun 2015 20:58:56 -0400 Received: from mail-lb0-f177.google.com ([209.85.217.177]:35046 "EHLO mail-lb0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751493AbbFCA6r (ORCPT ); Tue, 2 Jun 2015 20:58:47 -0400 MIME-Version: 1.0 In-Reply-To: <20150603003938.GQ1187@tassilo.jf.intel.com> References: <1432194944-29087-1-git-send-email-adrian.hunter@intel.com> <20150602194350.GN1187@tassilo.jf.intel.com> <20150602202037.GO1187@tassilo.jf.intel.com> <20150602233820.GP1187@tassilo.jf.intel.com> <20150603003938.GQ1187@tassilo.jf.intel.com> From: Andy Lutomirski Date: Tue, 2 Jun 2015 17:58:25 -0700 Message-ID: Subject: Re: [PATCH RFC] x86, tsc: Allow for high latency in quick_pit_calibrate() To: Andi Kleen Cc: Thomas Gleixner , Adrian Hunter , LKML , Linus Torvalds , X86 ML , "H. Peter Anvin" , Len Brown Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1593 Lines: 41 On Tue, Jun 2, 2015 at 5:39 PM, Andi Kleen wrote: > On Tue, Jun 02, 2015 at 05:21:27PM -0700, Andy Lutomirski wrote: >> On Tue, Jun 2, 2015 at 4:38 PM, Andi Kleen wrote: >> > On Tue, Jun 02, 2015 at 11:03:26PM +0200, Thomas Gleixner wrote: >> >> >> >> >> >> On Tue, 2 Jun 2015, Andi Kleen wrote: >> >> >> >> > > There's the code in tsc_msr.c. It should be relatively >> >> > > straightforward to extend it to cover everything that intel_pstate >> >> > > supports. >> >> > >> >> > That's a good idea, but we still need an always working fallback when the >> >> > model number is not available. So Adrian's patch is needed in any >> >> > case. >> >> >> >> Nonsense. The slow calibration is already a working fallback. >> > >> > Please read Adrian's description again. It's not working when the PIT read is >> > too slow. That is when the new algorithm is needed. >> > >> >> tglx's suggestion was to use slow calibration as a fallback. > > You mean the last fallback we have today? > > That one doesn't work if the PIT read is too slow. > > And Adrian's patch is fixing that. Then the changelog should say that I think. The current text says "Fast TSC calibration will always fail", which, to me, suggests that either the slow calibration will work or that the changelog message should be changed. --Andy -- 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/