From 6d1acfd5c6bfd5231c13a8f2858d7f2afbaa1b62 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 18 May 2010 11:12:48 +0200 Subject: [PATCH] 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 LKML-Reference: Signed-off-by: Ingo Molnar --- include/linux/perf_event.h | 1 + kernel/perf_event.c | 3 ++- 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index ce7667616fcb..fe50347dc645 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 1f98c78c3343..7e3bcf1a29f0 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(); -- 2.20.1