Re: [PATCH 86/98] ACPI: cap off P-state transition latency from buggy BIOSes

Len Brown
2009-04-03T16:35:40Z

> Whatabout:
>
> CC: stable@kernel.org

I've added this to my .stable list, thanks for pointing it out.
Note that I don't send patches to stable until after they are upstream.

thanks,
-Len

> This is a bug fix also existing in older kernels.
>
> I remember even much newer HW (Intel and AMD) based have higher values
>
> exported through ACPI _PSS tables as latency.
>
> I remember values around (50-70us Core 2 Duo?) and 37us on K10.
>
> I doubt this patch will cause much pain, but being close to values exported
>
> via ACPI tables on similar HW sounds like a good idea.
>
> In 2.6.30 (as soon as cpufreq branch is merged) you get that easily from here:
>
> cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_transition_latency
>
> 109000
>
> I expect my machine's (K8 Dual core) ACPI exported value will be cut down to:
>
> 20000
>
> now?

Does your AMD box run acpi-cpufreq and use native MSR access to change
P-states?

> I don't want to veto this one, but IMO the 20us second value
>
> should get 100us...

Where does 100us come from?

thanks,
-Len Brown, Intel Open Source Technology Center