From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Sigler Subject: Re: High resolution timers on ACPI-less kernel Date: Tue, 09 Oct 2007 11:39:08 +0200 Message-ID: <470B4C3C.3000406@free.fr> References: <470B44A1.7080007@free.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org To: Thomas Gleixner Cc: linux-rt-users@vger.kernel.org, linux-acpi@vger.kernel.org List-Id: linux-acpi@vger.kernel.org Thomas Gleixner wrote: > On Tue, 9 Oct 2007, John Sigler wrote: > >> I'm using a -rt kernel with high resolution timer support. >> http://rt.wiki.kernel.org/index.php/Main_Page >> Linux version 2.6.22.1-rt9 (root@venus) (gcc version 3.4.6) #1 PREEMPT RT Tue >> Oct 9 10:02:45 CEST 2007 >> >> I enabled high resolution timer support and disabled ACPI support. >> ... >> High resolution timers do not work in this configuration. > > Correct > >> Any idea why? > > Yes > >> # cat /sys/devices/system/clocksource/clocksource0/available_clocksource >> tsc pit jiffies >> >> # cat /sys/devices/system/clocksource/clocksource0/current_clocksource >> tsc >> >> My timestamp counter is good. Why do I need ACPI for hrt? > > We do not trust TSC at all. Never ever. > > The kernel refuses to switch to high resolution mode, when there is no > reliable backup clock source available. ACPI enables the acpi_pm > timer, which is a trusted clock source and is used by the kernel to > verify the correctness of the TSC. You might try to enable HPET. OK. I seem to remember that you had a patch to enable HPET on ICH4? Is it still available somewhere? Regards.