Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755557Ab3JBRmo (ORCPT ); Wed, 2 Oct 2013 13:42:44 -0400 Received: from smtp.codeaurora.org ([198.145.11.231]:34276 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755540Ab3JBRmm (ORCPT ); Wed, 2 Oct 2013 13:42:42 -0400 Message-ID: <524C5B10.20006@codeaurora.org> Date: Wed, 02 Oct 2013 10:42:40 -0700 From: Stephen Boyd User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: Santosh Shilimkar CC: Will Deacon , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "arm@kernel.org" , John Stultz , Russell King , "rob.herring@calxeda.com" , Thomas Gleixner , Daniel Lezcano Subject: Re: [PATCH] sched_clock: fix postinit no sched_clock function check References: <1380732928-13897-1-git-send-email-santosh.shilimkar@ti.com> <20131002170917.GB30298@mudshark.cambridge.arm.com> <524C5484.5000601@ti.com> <524C565C.8010709@codeaurora.org> <524C5786.2090008@ti.com> In-Reply-To: <524C5786.2090008@ti.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2695 Lines: 50 On 10/02/13 10:27, Santosh Shilimkar wrote: > On Wednesday 02 October 2013 01:22 PM, Stephen Boyd wrote: >> On 10/02/13 10:14, Santosh Shilimkar wrote: >>> On Wednesday 02 October 2013 01:09 PM, Will Deacon wrote: >>>> On Wed, Oct 02, 2013 at 05:55:28PM +0100, Santosh Shilimkar wrote: >>>>> The sched_clock code uses 2 levels of function pointers, sched_clock_func() >>>>> and read_sched_clock() but the no sched_clock check in postinit() just >>>>> checks read_sched_clock(). >>>>> >>>>> This leads to kernel falling back to jiffy based sched clock even in >>>>> presence of sched_clock_func() which is not desirable. >>>>> >>>>> Fix the postinit() check to avoid the issue. Probably the issue is hidden >>>>> so far on most of the arm SOCs because of already existing sched_clock >>>>> registrations apart from arch_timer sched_clock. One can reproduce the >>>>> issue by just have arch_timer as sched_clock >>>> Isn't this just an issue with the arch timer driver not calling >>>> setup_sched_clock? Instead, we munge around with sched_clock_func directly, >>>> which doesn't appear to be the way anybody else deals with this. >>>> >>> I thought about that option as well but was not sure since even in that case >>> the check is not complete. We just ensure that function is popullated. >> Yes, nothing is actually broken because sched_clock_func() won't try to >> use the jiffy based read_sched_clock() function. I'm not sure we >> actually need this patch besides to remove a useless timer that updates >> the jiffy epoch. Can we wait until my 64-bit sched_clock patch series >> lands in 3.13? It looks like I still need an ack from Will or Catalin on >> the architected timer patch before the clocksource folks pick it up. >> > Really... I have not created patch out of fun. > Its broken on my keystone machine at least where the sched_clock is > falling back on jiffy based sched_clock even in presence of arch_timer > sched_clock. How is that possible? sched_clock_func is only assigned by arch/arm/kernel/arch_timer.c when the architected timer is detected and sched_clock() in kernel/time/sched_clock.c calls that function pointer unconditionally. The only way I see this happening is if the architected timer rate is zero. I agree we will get two lines in the dmesg about sched_clock and its not very clear which one is being used. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- 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/