Messages in this thread Patch in this message | | | Date | Fri, 13 Mar 2009 13:01:06 GMT | From | Peter Zijlstra <> | Subject | [tip:perfcounters/core] perf_counter: add comment to barrier |
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Commit-ID: 1b1646b16f983a880163afb9efd296de01c7d854 Gitweb: http://git.kernel.org/tip/1b1646b16f983a880163afb9efd296de01c7d854 Author: Peter Zijlstra <a.p.zijlstra@chello.nl> AuthorDate: Fri, 13 Mar 2009 12:21:30 +0100 Commit: Ingo Molnar <mingo@elte.hu> CommitDate: Fri, 13 Mar 2009 13:59:08 +0100
perf_counter: add comment to barrier
We need to ensure the enabled=0 write happens before we start disabling the actual counters, so that a pcm_amd_enable() will not enable one underneath us.
I think the race is impossible anyway, we always balance the ops within any one context and perform enable() with IRQs disabled.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20090313112301.384074618@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
--- arch/x86/kernel/cpu/perf_counter.c | 4 ++++ 1 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c index 1cedc34..a2e3b76 100644 --- a/arch/x86/kernel/cpu/perf_counter.c +++ b/arch/x86/kernel/cpu/perf_counter.c @@ -247,6 +247,10 @@ static u64 pmc_amd_save_disable_all(void) enabled = cpuc->enabled; cpuc->enabled = 0; + /* + * ensure we write the disable before we start disabling the + * counters proper, so that pcm_amd_enable() does the right thing. + */ barrier(); for (idx = 0; idx < nr_counters_generic; idx++) {
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