[PATCH] powerpc: perf: power_pmu_start restores incorrect values, breaking frequency events

[Stephane Eranian]

Glad to see you fixed the PPC problem.

On Thu, Feb 16, 2012 at 5:57 AM, Paul Mackerras <paulus at samba.org> wrote:
> On Thu, Feb 16, 2012 at 03:48:22PM +1100, Anton Blanchard wrote:
>>
>> perf on POWER stopped working after commit e050e3f0a71b (perf: Fix
>> broken interrupt rate throttling). That patch exposed a bug in
>> the POWER perf_events code.
>>
>> Since the PMCs count upwards and take an exception when the top bit
>> is set, we want to write 0x80000000 - left in power_pmu_start. We were
>> instead programming in left which effectively disables the counter
>> until we eventually hit 0x80000000. This could take seconds or longer.
>>
>> With the patch applied I get the expected number of samples:
>>
>> # taskset -c 0 yes > /dev/null &
>> # perf record -C 0 -a sleep 10
>> # perf report -D | grep SAMPLE | tail -1
>>           SAMPLE events:       9948
>>
>> Signed-off-by: Anton Blanchard <anton at samba.org>
>
> Acked-by: Paul Mackerras <paulus at samba.org>