From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758427AbcBXRNF (ORCPT ); Wed, 24 Feb 2016 12:13:05 -0500 Received: from eusmtp01.atmel.com ([212.144.249.243]:49315 "EHLO eusmtp01.atmel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757609AbcBXRNB (ORCPT ); Wed, 24 Feb 2016 12:13:01 -0500 Subject: Re: [PATCH v2] clocksource: atmel-pit: register as a sched_clock To: Romain Izard , Sylvain Rochet References: <1456329882-20709-1-git-send-email-romain.izard.pro@gmail.com> <20160224162046.GA28743@finsecur.com> CC: LKML , , Boris Brezillon , Daniel Lezcano , Alexandre Belloni , Thomas Gleixner , Cyrille Pitchen From: Nicolas Ferre X-Enigmail-Draft-Status: N1110 Organization: atmel Message-ID: <56CDE4A4.7080508@atmel.com> Date: Wed, 24 Feb 2016 18:13:08 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.161.30.18] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 24/02/2016 17:44, Romain Izard a écrit : > 2016-02-24 17:20 GMT+01:00 Sylvain Rochet : >> Hi, >> >> On Wed, Feb 24, 2016 at 05:04:42PM +0100, Romain Izard wrote: >>> Register the counter of the Periodic Interval Timer as a possible >>> source for sched_clock. Keep the timer running even if the related >>> clockevent is disabled. >>> >>> This provides a better precision than the jiffies-based default. The >>> TCB clocksource does not work, as it is registered too late in the >>> initialization sequence. >> >> I have mixed feelings about that, but this is probably just a >> misunderstanding from my part. >> > My goal is to get a better precision on my printk and trace logs, > because the precision of jiffies is really very bad compared to > everything else I have encountered until now. But it looks like reading > a timer is quite complicated on AT91... > >> The PIT timer should not be used for systems with PM_SUSPEND enabled >> and used because it takes ages to synchronize on resume, how does this >> patch affect that ? >> >> Ref: commit ac34ad27fc ("clockevents: Do not suspend/resume if >> unused") > > So your advice would be to stay clear of the PIT, because it is > (globally) useless. > > I'll keep it in mind. I tend to think like this as well. I would like to simplify our timer handling on AT91 and stick with TC for this purpose. It has de disadvantage of being obliged to use a TC(block) for clockevent/clocksource and loose it if we want to do something else with it but I do think that it's worth it. If you want a modified TC driver that registers sched_clock, we can provide you one as a workaround before that we rework the TC driver completely. It has it's own flaws (like re-using a compatible string or preventing the use of the "tclib") but is certainly handy. Bye, -- Nicolas Ferre