From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Renninger Subject: Re: [PATCH 3/3] trace points: power: remove 'cpu_id' from trace_cpu_idle Date: Mon, 22 Aug 2011 10:27:34 +0200 Message-ID: <201108221027.34441.trenn@suse.de> References: <1313766244-22313-1-git-send-email-tom.leiming@gmail.com> <201108192231.02665.trenn@suse.de> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: Received: from cantor2.suse.de ([195.135.220.15]:47968 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756593Ab1HVI1i (ORCPT ); Mon, 22 Aug 2011 04:27:38 -0400 In-Reply-To: Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Ming Lei Cc: rostedt@goodmis.org, fweisbec@gmail.com, jean.pihet@newoldbits.com, mingo@redhat.com, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, Len Brown On Saturday, August 20, 2011 04:40:09 AM Ming Lei wrote: > Hi, > > 2011/8/20 Thomas Renninger : > > On Friday, August 19, 2011 05:04:04 PM tom.leiming@gmail.com wrote: > >> From: Ming Lei > >> > >> This patch removes the 'cpu_id' parameter of the cpu_idle > >> trace point, based on the ideas below: > >> > >> - the cpu_id which is passed to trace point is always the current > >> cpu > > Are you sure this will always be true? > > It is sure at least now, the only place to pass 'dev->cpu' is inside > cpuidle_idle_call, It was known that cpu_id is always the current cpu with current implementation when this got introduced. But the perf events API must not change back and forth for userspace compatibility. Therefore the cpu_id was added in case that future implementations want to pass info where the current cpu is not the cpu which is sent to the sleep state. > smp_processor_id() can't be used safely in preemptible context. I expect the only side effect that could happen is that if smp_process_id is interrupted you get the wrong core id on a cpu idle trace event. This only happens if cpuidle is not used and even then should happen very rarely, nothing to worry for a debug tool like that. And it should get fixed if these idle functions get fully integrated into cpuidle at some point of time. Thomas