Re: [BUG] APM resume breakage from 2.6.18-rc1 clocksource changes

[Mikael Pettersson <mikpe@it.uu.se>]

On Sun, 09 Jul 2006 17:31:39 -0400, Valdis.Kletnieks wrote:
>On Sun, 09 Jul 2006 22:58:31 +0200, Mikael Pettersson said:
>
>> I've traced the cause of this problem to the i386 time-keeping
>> changes in kernel 2.6.17-git11. What happens is that:
>> - The kernel autoselects TSC as my clocksource, which is
>>   reasonable since it's a PentiumII. 2.6.17 also chose the TSC.
>> - Immediately after APM resumes (arch/i386/kernel/apm.c line
>>   1231 in 2.6.18-rc1) there is an interrupt from the PIT,
>>   which takes us to kernel/timer.c:update_wall_time().
>> - update_wall_time() does a clocksource_read() and computes
>>   the offset from the previous read. However, the TSC was
>>   reset by HW or BIOS during the APM suspend/resume cycle and
>>   is now smaller than it was at the prevous read. On my machine,
>>   the offset is 0xffffffd598e0a566 at this point, which appears
>>   to throw update_wall_time() into a very very long loop.
>
>Does applying this patch make it work?
>
>ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.18-rc1/2.6.18-rc1-mm1/broken-out/adjust-clock-for-lost-ticks.patch
>
>Or is this a different breakage?

I haven't tried it, but I'm 99% certain it's unrelated breakage.
In my case the TSC jumped backwards not forwards as would be the
case in a lost ticks scenario, and the patch above doesn't touch
the code that gets into an semi-infinite loop in my case.

/Mikael
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