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Commit 6d1acfd5 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent fa588151

include/linux/perf_event.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

};

kernel/perf_event.c

+2 −1
Original line number Diff line number Diff line
@@ -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 @@ static void perf_output_put_handle(struct perf_output_handle *handle) 
		goto again;

	}



	if (local_xchg(&data->wakeup, 0))

	if (handle->wakeup != local_read(&data->wakeup))

		perf_output_wakeup(handle);



	preempt_enable();