perf: Optimize perf_output_begin() -- lost_event case

Avoid touching the lost_event and sample_data cachelines twince. Its
not like we end up doing less work, but it might help to keep all
accesses to these cachelines in one place.

Due to code shuffle, this looses 4 bytes on x86_64-defconfig.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: james.hogan@imgtec.com
Cc: Vince Weaver <vince@deater.net>
Cc: Victor Kaplansky <VICTORK@il.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Anton Blanchard <anton@samba.org>
Link: http://lkml.kernel.org/n/tip-zfxnc58qxj0eawdoj31hhupv@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 8 insertions, 5 deletions

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 6ed16ecfd0a3..e4d70f33792f 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -106,7 +106,6 @@ int perf_output_begin(struct perf_output_handle *handle,
         struct ring_buffer *rb;
         unsigned long tail, offset, head;
         int have_lost;
-        struct perf_sample_data sample_data;
         struct {
                 struct perf_event_header header;
                 u64                      id;
@@ -132,10 +131,9 @@ int perf_output_begin(struct perf_output_handle *handle,
 
         have_lost = local_read(&rb->lost);
         if (unlikely(have_lost)) {
-                lost_event.header.size = sizeof(lost_event);
-                perf_event_header__init_id(&lost_event.header, &sample_data,
-                                           event);
-                size += lost_event.header.size;
+                size += sizeof(lost_event);
+                if (event->attr.sample_id_all)
+                        size += event->id_header_size;
         }
 
         perf_output_get_handle(handle);
@@ -169,11 +167,16 @@ int perf_output_begin(struct perf_output_handle *handle,
         handle->size = (PAGE_SIZE << page_order(rb)) - handle->size;
 
         if (unlikely(have_lost)) {
+                struct perf_sample_data sample_data;
+
+                lost_event.header.size = sizeof(lost_event);
                 lost_event.header.type = PERF_RECORD_LOST;
                 lost_event.header.misc = 0;
                 lost_event.id          = event->id;
                 lost_event.lost        = local_xchg(&rb->lost, 0);
 
+                perf_event_header__init_id(&lost_event.header,
+                                           &sample_data, event);
                 perf_output_put(handle, lost_event);
                 perf_event__output_id_sample(event, handle, &sample_data);
         }