Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752693Ab3IJPOV (ORCPT ); Tue, 10 Sep 2013 11:14:21 -0400 Received: from mail-oa0-f44.google.com ([209.85.219.44]:48681 "EHLO mail-oa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751480Ab3IJPOS (ORCPT ); Tue, 10 Sep 2013 11:14:18 -0400 MIME-Version: 1.0 In-Reply-To: <4292924.3iHJT5nzNS@vostro.rjw.lan> References: <4292924.3iHJT5nzNS@vostro.rjw.lan> Date: Tue, 10 Sep 2013 20:44:18 +0530 Message-ID: Subject: Re: "cpufreq: fix serialization issues with freq change notifiers" breaks cpufreq too From: Viresh Kumar To: "Rafael J. Wysocki" Cc: Guennadi Liakhovetski , Greg KH , "Rafael J. Wysocki" , Linux Kernel Mailing List , "linux-arm-kernel@lists.infradead.org" , "linux-pm@vger.kernel.org" , "cpufreq@vger.kernel.org" , SH-Linux , Magnus Damm Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1779 Lines: 38 On 10 September 2013 17:19, Rafael J. Wysocki wrote: > That said I'm actually unsure what problems *exactly* are fixed by commit > 7c30ed5. The commit log only says that PRECHANGE or POSTCHAGE shouldn't be > called twice in a row, but it doesn't say why. As the fallout indicates, > that actually happened before commit 7c30ed5 and nothing visibly broke, so > the benefit from having that commit is questionable to me. On the other hand, > the commit itself is evidently broken, so what exactly is the reason for > keeping it? Okay, so the first question is can we have multiple PRECHANGE notfication done without any POSTCHANGE inbetween? - Scenario: One reading value of cpuinfo_cur_freq, which will call __cpufreq_cpu_get()->cpufreq_out_of_sync()->cpufreq_notify_transition().. And ondemand governor trying to change freq of cpu and so doing notification.. There can be more similar scenarios possible.. Now Second question, is this fine to have multiple PRECHANGE notfications before any POSTCHANGE notification? Logically it looks obvious to me that these must be serialized.. Otherwise this is what we are broadcasting: - We are changing for freq X, please prepare and let us know if you are okay with it.. - Oh.. So sorry, we are changing to freq Y instead, please adjust accordingly. - Yes we have changed to freq Y... - Yes we have changed to freq X... This looks stupid, isn't it? I don't know how the drivers would behave when they see such notifications and so got to this patch initially.. -- 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/