commit ec5e099d6e941668d121ea9ca7057f4fa00830b0
author Alexei Starovoitov <ast@fb.com> Wed Apr 06 18:43:22 2016 -0700
committer David S. Miller <davem@davemloft.net> Thu Apr 07 21:04:26 2016 -0400
tree 4ec273d88501a68ce23eb53649530161a7fa8440
parent b33b0a1bf69faff89693df49519fa7b459f5d807

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/trace/trace_event_perf.c

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 00df25f..7a68afc 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -316,6 +316,7 @@
 
 	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);