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authorPeter Zijlstra <peterz@infradead.org>2013-10-31 17:20:25 +0100
committerIngo Molnar <mingo@kernel.org>2013-11-06 12:34:19 +0100
commitc72b42a3dde487132da80202756c101b371b2add (patch)
tree5e6771876f565957aae8caab8e6abddba707f5be /kernel/events
parent26c86da8821f7b64fced498674990318bc34c8de (diff)
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@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-wlg3jew3qnutm8opd0hyeuwn@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/events')
-rw-r--r--kernel/events/ring_buffer.c16
1 files changed, 8 insertions, 8 deletions
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 6929c5848d4f..383cde476176 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;