Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752256AbZKLINY (ORCPT ); Thu, 12 Nov 2009 03:13:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751864AbZKLINY (ORCPT ); Thu, 12 Nov 2009 03:13:24 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:35748 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751631AbZKLINX (ORCPT ); Thu, 12 Nov 2009 03:13:23 -0500 Date: Thu, 12 Nov 2009 09:13:17 +0100 From: Ingo Molnar To: "H. Peter Anvin" Cc: Bartlomiej Zolnierkiewicz , x86@kernel.org, linux-kernel@vger.kernel.org, Dave Jones Subject: Re: [PATCH RFC] x86: fix confusing name of /proc/cpuinfo "ht" flag Message-ID: <20091112081317.GB25345@elte.hu> References: <200911112134.34261.bzolnier@gmail.com> <20091112065930.GA9279@elte.hu> <4AFBB45A.9000606@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AFBB45A.9000606@zytor.com> User-Agent: Mutt/1.5.20 (2009-08-17) 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 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1345 Lines: 35 * H. Peter Anvin wrote: > On 11/11/2009 10:59 PM, Ingo Molnar wrote: > > > > * Bartlomiej Zolnierkiewicz wrote: > > > >> "ht" flag indicates only ability to detect siblings not HT presence > >> itself. > >> > >> Inspired by: > >> http://www.codemonkey.org.uk/2009/11/10/common-hyperthreading-misconception/ > > > > i think instead of changing 'ht' to 'ht_detect', it would be even > > more intuitive to only expose the 'ht' flag if the ht-detect > > capability is there _and_ if the number of siblings is 2 or more. > > > > That way we dont change it - we just 'hide' the 'ht' string on the > > category of systems that can enumerate HT via the CPUID but dont > > actually have HyperThreading. > > /proc/cpuinfo is a user-space visible ABI. Changing it is bad > chicken. Almost ... something is only an ABI if an actual application relies on the 'ht' flag being there on non-hyperthreading CPUs. We dont know whether there's any, but the likelyhood looks pretty low. Could park it a branch for some time to see whether anything trips up. Ingo -- 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/