powerpc/perf: power_pmu_start restores incorrect values, breaking frequency events
authorAnton Blanchard <anton@samba.org>
Wed, 15 Feb 2012 18:48:22 +0000 (18:48 +0000)
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>
Thu, 16 Feb 2012 05:24:35 +0000 (16:24 +1100)
commit9a45a9407c69d068500923480884661e2b9cc421
tree8ff43b5fd98ab68352dc4dd0823401a5736afab2
parent64f8c13561fbd2f1a8b4a8975b2aee73b561093e
powerpc/perf: power_pmu_start restores incorrect values, breaking frequency events

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:

          SAMPLE events:       9948

Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: <stable@kernel.org>
arch/powerpc/kernel/perf_event.c