From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752673AbdLHHwS (ORCPT ); Fri, 8 Dec 2017 02:52:18 -0500 Received: from mail-wr0-f195.google.com ([209.85.128.195]:46478 "EHLO mail-wr0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752387AbdLHHwQ (ORCPT ); Fri, 8 Dec 2017 02:52:16 -0500 X-Google-Smtp-Source: AGs4zMbX6NBLDPXF0RS7CMjD+nhdvq4m/cujDlgAJ+QftKPUS+Q+6GqDerNE0byiLYg9ZGZdCuMsEw== Subject: Re: [PATCH v8 4/6] clocksource: stm32: only use 32 bits timers To: Benjamin Gaignard Cc: Rob Herring , Mark Rutland , Russell King - ARM Linux , Maxime Coquelin , Alexandre Torgue , Thomas Gleixner , Ludovic Barre , Julien Thierry , Sudeep Holla , Arnd Bergmann , devicetree@vger.kernel.org, Linux ARM , Linux Kernel Mailing List References: <1510649563-22975-1-git-send-email-benjamin.gaignard@linaro.org> <1510649563-22975-5-git-send-email-benjamin.gaignard@linaro.org> <44bb54e6-c9e8-4b54-d490-a1800bf6d74c@linaro.org> <2afa343b-3a23-3352-33b3-2133678a4122@linaro.org> From: Daniel Lezcano Message-ID: <4f9ed3dd-cf02-eed7-7fdd-38f8dc092eee@linaro.org> Date: Fri, 8 Dec 2017 08:52:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/12/2017 21:36, Benjamin Gaignard wrote: > 2017-12-07 17:49 GMT+01:00 Daniel Lezcano : >> On 07/12/2017 17:33, Benjamin Gaignard wrote: >>> 2017-12-07 16:27 GMT+01:00 Daniel Lezcano : >>>> On 14/11/2017 09:52, Benjamin Gaignard wrote: >>>>> The clock driving counters is at 90MHz so the maximum period >>>>> for 16 bis counters is around 750 ms which is a short period >>>>> for a clocksource. >>>> >>>> Isn't it 728us ? >>> >>> yes it is: 2^16 / 90.000.000 => 728us >> >> Ok, now I can do the connection with the previous patch. >> >> So, the real issue of all this is the 16bits clocksource is wrapping up >> every 728us, hence the clockevent periodically expires every ~728us to >> keep the timekeeping consistent. Unfortunately, the kernel has a too >> high overhead for this as the system is consistently processing this >> timer leading to a CPU time resource starvation. >> >> Is that correct ? > > Yes that is correct Oh man. That was unclear since the beginning, we are not talking about inaccurate clocksource or whatever but just these 16bits timers can't work on Linux. -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog