Messages in this thread Patch in this message | | | Date | Tue, 18 May 2010 15:33:02 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 4/5] perf: Avoid local_xchg |
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Since the x86 XCHG ins implies LOCK, avoid the use by using a sequence count instead.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> --- include/linux/perf_event.h | 1 + kernel/perf_event.c | 3 ++- 2 files changed, 3 insertions(+), 1 deletion(-)
Index: linux-2.6/include/linux/perf_event.h =================================================================== --- linux-2.6.orig/include/linux/perf_event.h +++ linux-2.6/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; }; Index: linux-2.6/kernel/perf_event.c =================================================================== --- linux-2.6.orig/kernel/perf_event.c +++ linux-2.6/kernel/perf_event.c @@ -2917,6 +2917,7 @@ static void perf_output_get_handle(struc 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();
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