perf: Optimize perf_output_begin() -- address calculation

Rewrite the handle address calculation code to be clearer.

Saves 8 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-3trb2n2henb9m27tncef3ag7@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 7 insertions, 7 deletions

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index e4d70f33792f..c52a32fa5592 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -105,7 +105,7 @@ int perf_output_begin(struct perf_output_handle *handle,
 {
         struct ring_buffer *rb;
         unsigned long tail, offset, head;
-        int have_lost;
+        int have_lost, page_shift;
         struct {
                 struct perf_event_header header;
                 u64                      id;
@@ -159,12 +159,12 @@ int perf_output_begin(struct perf_output_handle *handle,
         if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
                 local_add(rb->watermark, &rb->wakeup);
 
-        handle->page = offset >> (PAGE_SHIFT + page_order(rb));
-        handle->page &= rb->nr_pages - 1;
-        handle->size = offset & ((PAGE_SIZE << page_order(rb)) - 1);
-        handle->addr = rb->data_pages[handle->page];
-        handle->addr += handle->size;
-        handle->size = (PAGE_SIZE << page_order(rb)) - handle->size;
+        page_shift = PAGE_SHIFT + page_order(rb);
+
+        handle->page = (offset >> page_shift) & (rb->nr_pages - 1);
+        offset &= (1UL << page_shift) - 1;
+        handle->addr = rb->data_pages[handle->page] + offset;
+        handle->size = (1UL << page_shift) - offset;
 
         if (unlikely(have_lost)) {
                 struct perf_sample_data sample_data;