From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754710AbYKRQGM (ORCPT ); Tue, 18 Nov 2008 11:06:12 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752595AbYKRQF6 (ORCPT ); Tue, 18 Nov 2008 11:05:58 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:48634 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752165AbYKRQF6 (ORCPT ); Tue, 18 Nov 2008 11:05:58 -0500 Date: Tue, 18 Nov 2008 17:05:42 +0100 From: Ingo Molnar To: Joe Korty Cc: Venki Pallipadi , H Peter Anvin , Thomas Gleixner , linux-kernel Subject: Re: [PATCH] x86: Support always running TSC on Intel CPUs Message-ID: <20081118160542.GC8088@elte.hu> References: <20081118001137.GA12350@linux-os.sc.intel.com> <20081118080952.GE17838@elte.hu> <20081118145540.GA32082@tsunami.ccur.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081118145540.GA32082@tsunami.ccur.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00,DNS_FROM_SECURITYSAGE autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] 0.0 DNS_FROM_SECURITYSAGE RBL: Envelope sender in blackholes.securitysage.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Joe Korty wrote: > On Tue, Nov 18, 2008 at 09:09:52AM +0100, Ingo Molnar wrote: > > > > * Venki Pallipadi wrote: > > > > > + if (c->x86_power & (1 << 8)) { > > > set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); > > > + set_cpu_cap(c, X86_FEATURE_NOSTOP_TSC); > > > + } > > > > hm, the naming is a bit confusing. We now have 3 variants: > > > > X86_FEATURE_TSC > > X86_FEATURE_CONSTANT_TSC > > X86_FEATURE_NOSTOP_TSC > > > > NOSTOP_TSC is basically what CONSTANT_TSC should have been to begin > > with ;-) > > > > i'd suggest to rename it to this: > > > > X86_FEATURE_TSC > > X86_FEATURE_CONSTANT_FREQ_TSC > > X86_FEATURE_STABLE_TSC > > > > ... with CONSTANT_FREQ_TSC not having any real role in the long run. > > (it's similarly problematic to a completely unstable TSC) > > > > does this sound ok? > > > To me, the new naming has the same head-scratching potential > as the old.... > > How about: > > X86_FEATURE_TSC > X86_FEATURE_STABLE_TSC_OBSOLETE > X86_FEATURE_STABLE_TSC the _honest_ naming would be: X86_FEATURE_TSC X86_FEATURE_STABLE_TSC_BUT_NOT_ALWAYS X86_FEATURE_STABLE_TSC ;-) what's head-scratching about X86_FEATURE_CONSTANT_FREQ_TSC? It's a limited TSC variant: it follows a reference frequency that does not change with cpufreq changes, but it can stop at a whim in C states. So it's not "stable" nor really "constant" in the everyday sense. What is 'constant' about it is its reference frequency - hence X86_FEATURE_CONSTANT_FREQ_TSC. Ingo