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[PATCH v2 net-next 01/10] perf: optimize perf_fetch_caller_regs

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  [PATCH v2 net-next 01/10] perf: optimize perf_fetch_caller_regs Alexei Starovoitov <ast@fb.com> - 2016-04-07 03:50 +0200

#1373012 — [PATCH v2 net-next 01/10] perf: optimize perf_fetch_caller_regs

avoid memset in perf_fetch_caller_regs, since it's the critical path of all tracepoints.
It's called from perf_sw_event_sched, perf_event_task_sched_in and all of perf_trace_##call
with this_cpu_ptr(&__perf_regs[..]) which are zero initialized by perpcu init logic and
subsequent call to perf_arch_fetch_caller_regs initializes the same fields on all archs,
so we can safely drop memset from all of the above cases and move it into
perf_ftrace_function_call that calls it with stack allocated pt_regs.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/perf_event.h      | 2 --
 kernel/trace/trace_event_perf.c | 1 +
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f291275ffd71..e89f7199c223 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -882,8 +882,6 @@ static inline void perf_arch_fetch_caller_regs(struct pt_regs *regs, unsigned lo
  */
 static inline void perf_fetch_caller_regs(struct pt_regs *regs)
 {
-	memset(regs, 0, sizeof(*regs));
-
 	perf_arch_fetch_caller_regs(regs, CALLER_ADDR0);
 }
 
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 00df25fd86ef..7a68afca8249 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -316,6 +316,7 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
 
 	BUILD_BUG_ON(ENTRY_SIZE > PERF_MAX_TRACE_SIZE);
 
+	memset(&regs, 0, sizeof(regs));
 	perf_fetch_caller_regs(&regs);
 
 	entry = perf_trace_buf_prepare(ENTRY_SIZE, TRACE_FN, NULL, &rctx);
-- 
2.8.0

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