From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753796AbbAEMdG (ORCPT ); Mon, 5 Jan 2015 07:33:06 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:55292 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753298AbbAEMdD (ORCPT ); Mon, 5 Jan 2015 07:33:03 -0500 Date: Mon, 5 Jan 2015 12:32:52 +0000 From: Will Deacon To: "Theodore Ts'o" , Russell King - ARM Linux , Nicolas Pitre , Linus Torvalds , Pavel Machek , Marc Zyngier , kernel list , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] Revert 9fc2105aeaaf56b0cf75296a84702d0f9e64437b to fix pyaudio (and probably more) Message-ID: <20150105123252.GB10116@arm.com> References: <20150104190123.GA20153@amd> <20150104201026.GA23427@amd> <20150104203724.GA16372@amd> <20150104212659.GC12302@n2100.arm.linux.org.uk> <20150105013436.GA23350@thunk.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150105013436.GA23350@thunk.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ted, On Mon, Jan 05, 2015 at 01:34:36AM +0000, Theodore Ts'o wrote: > On Sun, Jan 04, 2015 at 09:26:59PM +0000, Russell King - ARM Linux wrote: > > > > With the revert in place, we now have insanely small bogomips values > > reported via /proc/cpuinfo when hardware timers are used. That needs > > fixing. > > Why does it need to be fixed? > > It's clear that there are applications that are working OK with the > existing value, I'm not sure it is that clear -- the reported regression was on a processor that doesn't use the timer-backed delay loop, so the bogomips value will essentially be restored by reverting the patch. The issue comes on newer CPUs, where there will now be a very small bogomips value reported and (to my knowledge) nobody has yet tried running some affected applications there to see if they can cope. > and if you change it to fix it for some new applications, but it breaks > for others, then have you considered defining a new interface (perhaps > exported via sysfs) that exports a "sane" value and document that new > applications shoud use the new interface. > > Or if the answer is that no one should be using the bogomips field at > all, then just document *that*, and then leave it be, so that existing > applications don't break. It never hurts to document our assumptions or anticipated/preferred use-cases but in this case I think bogomips is difficult enough to use on any half-recent SoCs that most developers have either (a) found another way to do what they want (perf counters, clock_gettime) or (b) stopped bothering to guess the CPU frequency when it's not actually needed, so I don't *think* that new applications are such an issue. Cheers, Will