Commit-ID: c72b42a3dde487132da80202756c101b371b2add
Gitweb: http://git.kernel.org/tip/c72b42a3dde487132da80202756c101b371b2add
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 31 Oct 2013 17:20:25 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 6 Nov 2013 12:34:19 +0100
perf: Add unlikely() to the ring-buffer code
Add unlikely() annotations to 'slow' paths:
When having a sampling event but no output buffer; you have bigger
issues -- also the bail is still faster than actually doing the work.
When having a sampling event but a control page only buffer, you have
bigger issues -- again the bail is still faster than actually doing
work.
Optimize for the case where you're not loosing events -- again, not
doing the work is still faster but make sure that when you have to
actually do work its as fast as possible.
The typical watermark is 1/2 the buffer size, so most events will not
take this path.
Shrinks perf_output_begin() by 16 bytes on x86_64-defconfig.
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
Cc: Michael Ellerman <michael@xxxxxxxxxxxxxx>
Cc: Michael Neuling <mikey@xxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: james.hogan@xxxxxxxxxx
Cc: Vince Weaver <vince@xxxxxxxxxx>
Cc: Victor Kaplansky <VICTORK@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Anton Blanchard <anton@xxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-wlg3jew3qnutm8opd0hyeuwn@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/events/ring_buffer.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 6929c58..383cde4 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -121,17 +121,17 @@ int perf_output_begin(struct perf_output_handle *handle,
event = event->parent;
rb = rcu_dereference(event->rb);
- if (!rb)
+ if (unlikely(!rb))
goto out;
- handle->rb = rb;
- handle->event = event;
-
- if (!rb->nr_pages)
+ if (unlikely(!rb->nr_pages))
goto out;
+ handle->rb = rb;
+ handle->event = event;
+
have_lost = local_read(&rb->lost);
- if (have_lost) {
+ if (unlikely(have_lost)) {
lost_event.header.size = sizeof(lost_event);
perf_event_header__init_id(&lost_event.header, &sample_data,
event);
@@ -157,7 +157,7 @@ int perf_output_begin(struct perf_output_handle *handle,
head += size;
} while (local_cmpxchg(&rb->head, offset, head) != offset);
- if (head - local_read(&rb->wakeup) > rb->watermark)
+ if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
local_add(rb->watermark, &rb->wakeup);
handle->page = offset >> (PAGE_SHIFT + page_order(rb));
@@ -167,7 +167,7 @@ int perf_output_begin(struct perf_output_handle *handle,
handle->addr += handle->size;
handle->size = (PAGE_SIZE << page_order(rb)) - handle->size;
- if (have_lost) {
+ if (unlikely(have_lost)) {
lost_event.header.type = PERF_RECORD_LOST;
lost_event.header.misc = 0;
lost_event.id = event->id;
--
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