Re: [PATCH] Add PPC_FEATURE_PMU_COMPAT

[Maynard Johnson <maynardj@us.ibm.com>]

Nathan Lynch wrote:
> Kumar Gala wrote:
>   
>> On Jul 3, 2008, at 6:20 PM, Nathan Lynch wrote:
>>
>>     
>>> Beginning with Power6, there is a set of 32 PMU events which is
>>> compatible across POWER processor lines.  PPC_FEATURE_PMU_COMPAT
>>> indicates support for this subset.
>>>
>>> Signed-off-by: Nathan Lynch <ntl@pobox.com>
>>> ---
>>> arch/powerpc/kernel/cputable.c |    4 ++--
>>> include/asm-powerpc/cputable.h |    1 +
>>> 2 files changed, 3 insertions(+), 2 deletions(-)
>>>       
>> Can you explain what these PMU events are a bit further?
>>     
>
> Maynard, can you help out here...?  :)
>   
As of POWER6, a set of 32 common events were defined that must be
supported on all future POWER processors -- aka "PMU compat set".  The
main impetus for this compat set is the need to support partition
migration, especially from processor P(n) to processor P(n+1), where
performance software that's running in the new partition may not be
knowledgeable about processor P(n+1).  If a performance tool determines
it does not support the physical processor, but is told (via the
PPC_FEATURE_PMU_COMPAT bit) that the processor supports the notion of
the PMU compat set, then the performance tool can surface just those
events to the user of the tool.

Hope that helps.

-Maynard