From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: Re: gettimeofday() moving backwards Date: Thu, 19 Dec 2002 01:09:44 +0100 Sender: acpi-devel-admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Message-ID: <20021219000944.GF705@elf.ucw.cz> References: <1040241199.3e00d22fe594b@sms.ed.ac.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1040241199.3e00d22fe594b-Y3tGgqFSo3OFxr2TtlUqVg@public.gmane.org> Errors-To: acpi-devel-admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Help: List-Post: List-Subscribe: , List-Unsubscribe: , List-Archive: To: Paul Richards Cc: acpi-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: linux-acpi@vger.kernel.org Hi! > I am using linux kernel v2.4.20 with ACPI patch dated 2002-12-05. > > I have noticed that if my processor changes state (800Mhz up to 1200Mhz say) > then gettimeofday() behaves weirdly. It runs smoothly but every now and again > (on the order of 10 times a second) it makes a correction. If I have gone from > 800Mhz to 1200Mhz then the correction is backwards, otherwise it makes a forward > jump.. > > I presume that this is because the kernel hasn't noticed that the cpu state has > changed and hasn't corrected the variables that control how the time is > calculated using the tsc. > > Is there a patch for this..? It doesn't sound like *too* big a thing.. ie just > recalculate a cpl of timing variables when the cpu state changes.. but ofc I > don't know the details :) Its actually pretty hard to do... Because at least at APM cpu can change clock any time. And recalibration of delay loop takes quite long... Still it might be good idea to recalibrate after clock change. Pavel -- Worst form of spam? Adding advertisment signatures ala sourceforge.net. What goes next? Inserting advertisment *into* email? ------------------------------------------------------- This SF.NET email is sponsored by: Geek Gift Procrastinating? Get the perfect geek gift now! Before the Holidays pass you by. T H I N K G E E K . C O M http://www.thinkgeek.com/sf/