Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933863Ab1CaISt (ORCPT ); Thu, 31 Mar 2011 04:18:49 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:43821 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754097Ab1CaISq (ORCPT ); Thu, 31 Mar 2011 04:18:46 -0400 Date: Thu, 31 Mar 2011 10:18:00 +0200 From: Ingo Molnar To: Len Brown Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-pm@lists.linux-foundation.org, Len Brown , Linus Torvalds , Andrew Morton , Thomas Gleixner , "H. Peter Anvin" Subject: Re: [PATCH 2/9] x86 idle: remove NOP cpuinfo_x86.hlt_works_ok flag Message-ID: <20110331081800.GH5938@elte.hu> References: <67e90d97e0a77df4acd0c75e1bacc7714e011f3e.1301550524.git.len.brown@intel.com> <20110331061247.GA24786@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes 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: 2063 Lines: 58 * Len Brown wrote: > > > hlt_works_ok was X86_32 only, initialized to 1, and never cleared. > > > > > > On 32-bit kernels, this deletes a line from /proc/cpuinfo: "hlt_bug : no" > > > > I think you missed the valid usecase where an old CPU with broken halt is > > booted with the no-hlt boot parameter and does not want to crash in the HLT > > instruction. > > > > That "no-hlt" boot parameter does: > > > > arch/x86/kernel/cpu/bugs.c: boot_cpu_data.hlt_works_ok = 0; > > > > We can restrict compatibility, but *please* lets do it *explicitly*, not under > > some 'remove unused code' pretense ... > > > > Could you please list all CPU models that are affected? > > "no-hlt" existed only for 32-bit, and there were exactly zero > automatic invocations of it. Do we know whether a distro adds this to the boot line? Do we know about users relying on it. > "idle=poll" does the same thing -- sans change a line > in /proc/cpuinfo. It also has an effect on halt/poweroff, right? > Do we really need both? Probably not, as i said i do not disagree - i just think it should be more explicit. Make it a: "users of CPU models X beware" commit title, not 'remove inactive code' ... So please list the affected hardware and list the affected boot parameter explicitly, in a well-titled commit that phases out this (very likely unused) compatibility hack and *document* the idle=poll workaround for ancient hardware. There's still i386DX CPUs being manufactured these days - a 20+ years old CPU design is surprisingly resilient to spurious patent claims, for obvious reasons. Really, there's no need to do things by stealth. There's few things worse than doing the right thing for the wrong reason - it becomes a bad habit of subtly broken thinking quickly. Thanks, 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/