From: John Sigler <linux.kernel@free.fr>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-rt-users@vger.kernel.org, linux-acpi@vger.kernel.org
Subject: Re: High resolution timers on ACPI-less kernel
Date: Tue, 09 Oct 2007 11:39:08 +0200 [thread overview]
Message-ID: <470B4C3C.3000406@free.fr> (raw)
In-Reply-To: <alpine.LFD.0.9999.0710091117020.25146@localhost.localdomain>
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.
next prev parent reply other threads:[~2007-10-09 9:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-09 9:06 High resolution timers on ACPI-less kernel John Sigler
2007-10-09 9:15 ` Alessio Igor Bogani
2007-10-09 9:28 ` John Sigler
2007-10-09 9:34 ` Thomas Gleixner
2007-10-09 10:35 ` John Sigler
2007-10-09 15:59 ` Dragan Noveski
2007-10-09 17:13 ` Thomas Gleixner
2007-10-11 10:37 ` Dragan Noveski
2007-10-09 9:20 ` John Sigler
2007-10-09 9:22 ` Thomas Gleixner
2007-10-09 9:39 ` John Sigler [this message]
2007-10-09 9:48 ` Alessio Igor Bogani
2007-10-09 9:53 ` Thomas Gleixner
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