Re: [PATCH 7/8] cpufreq: Remove support for hardware P-state chipsfrom powernow-k8
From: Andre Przywara
Date: Wed Aug 22 2012 - 09:43:03 EST
On 08/22/2012 03:00 AM, Thomas Renninger wrote:
On Monday 20 August 2012 22:49:16 Rafael J. Wysocki wrote:
On Monday, August 20, 2012, Andre Przywara wrote:
On 08/05/2012 11:33 PM, Rafael J. Wysocki wrote:
On Thursday, July 26, 2012, Andre Przywara wrote:
...
If you insist, I can keep the code in powernow-k8, but it probably
wouldn't receive any support anymore and would increase confusion on the
user side.
I'm not afraid of that. And as I said, you can just add info messages to
powernow-k8 saying that the feature is deprecated and will be removed in the
future and _then_ you actually _can_ remove it in the future (say, 2-3 major
kernel releasew from now).
Full code duplication in powernow-k8 and acpi-cpufreq does not make sense
to me.
You would need extra logic that only the first is successfully loaded etc.
IMO this has more risk of introducing new bugs than any good.
A message like that might be useful though:
if (boot_cpu_has(X86_FEATURE_HW_PSTATE))
{
printk("powernowk8 does not serve MSR based frequency switching anymore, use acpi-cpufreq instead\n");
return -1;
}
Matthew had something even better, that is patch 3/8:
+ if (static_cpu_has(X86_FEATURE_HW_PSTATE))
+ request_module("acpi_cpufreq");
So if someone tries to load powernow-k8 on a recent CPU, it will
automatically load acpi-cpufreq instead.
I just realized that this doesn't work as expected, because powernow-k8
bails out early due to only family 0xf being in the matching CPUID
family list. Will fix this.
I will do some tests now to check our options:
1. A combination of Matthew's and Thomas' ideas: if powernow-k8 is
loaded on newer CPUs, request acpi-cpufreq to load _plus_ write a
warning that powernow-k8 is obsolete for this hardware. Don't load
powernow-k8 (which has support removed anyway). My favorite.
2. Add code (probably to the generic cpufreq framework) to avoid loading
two drivers. Print a warning if tried anyways. Leave h/w P-state support
in powernow-k8. It seems like that acpi-cpufreq takes precedence over
powernow-k8 in distribution's module load list, so this should work as
expected even with keeping the support in powernow-k8 (as a fallback in
case of trouble).
Regards,
Andre.
This would show people with init scripts that try to load cpufreq drivers
manually that they are not needed anymore. acpi-cpufreq should have been
loaded automatically already and cpufreq should be active.
Thomas
--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
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