From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [PATCH v8 4/6] clocksource: stm32: only use 32 bits timers Date: Fri, 8 Dec 2017 08:52:12 +0100 Message-ID: <4f9ed3dd-cf02-eed7-7fdd-38f8dc092eee@linaro.org> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: Content-Language: en-US Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linux ARM , Linux Kernel Mailing List List-Id: devicetree@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 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html