tree 4ded8d6858a4e50f0e3401e5e3f2a6c37fee8f58
parent 5872bdb88a35fae7d224bd6b21e5f377e854ccfc
author Peter Zijlstra <a.p.zijlstra@chello.nl> 1238663524 +0200
committer Ingo Molnar <mingo@elte.hu> 1239003047 +0200

perf_counter: update mmap() counter read

Paul noted that we don't need SMP barriers for the mmap() counter read
because its always on the same cpu (otherwise you can't access the hw
counter anyway).

So remove the SMP barriers and replace them with regular compiler
barriers.

Further, update the comment to include a race free method of reading
said hardware counter. The primary change is putting the pmc_read
inside the seq-loop, otherwise we can still race and read rubbish.

Noticed-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Orig-LKML-Reference: <20090402091319.577951445@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>