[tip:perf/core] perf: Optimize perf_output_*() by avoiding local_xchg()
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From: tip-bot for Peter Zijlstra on 18 May 2010 13:20 Commit-ID: 6d1acfd5c6bfd5231c13a8f2858d7f2afbaa1b62 Gitweb: http://git.kernel.org/tip/6d1acfd5c6bfd5231c13a8f2858d7f2afbaa1b62 Author: Peter Zijlstra <a.p.zijlstra(a)chello.nl> AuthorDate: Tue, 18 May 2010 11:12:48 +0200 Committer: Ingo Molnar <mingo(a)elte.hu> CommitDate: Tue, 18 May 2010 18:35:49 +0200 perf: Optimize perf_output_*() by avoiding local_xchg() Since the x86 XCHG ins implies LOCK, avoid the use by using a sequence count instead. Signed-off-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo(a)elte.hu> --- include/linux/perf_event.h | 1 + kernel/perf_event.c | 3 ++- 2 files changed, 3 insertions(+), 1 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index ce76676..fe50347 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -804,6 +804,7 @@ struct perf_output_handle { struct perf_mmap_data *data; unsigned long head; unsigned long offset; + unsigned long wakeup; int nmi; int sample; }; diff --git a/kernel/perf_event.c b/kernel/perf_event.c index 1f98c78..7e3bcf1 100644 --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -2917,6 +2917,7 @@ static void perf_output_get_handle(struct perf_output_handle *handle) preempt_disable(); local_inc(&data->nest); + handle->wakeup = local_read(&data->wakeup); } static void perf_output_put_handle(struct perf_output_handle *handle) @@ -2950,7 +2951,7 @@ again: goto again; } - if (local_xchg(&data->wakeup, 0)) + if (handle->wakeup != local_read(&data->wakeup)) perf_output_wakeup(handle); preempt_enable(); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |