3.10-stable review patch. If anyone has any objections, please let me know.
------------------
From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
commit f5c936c0f267ec58641451cf8b8d39b4c207ee4d upstream.
As now each semaphore has its own spinlock and parallel operations are
possible, give each semaphore its own cacheline.
On a i3 laptop, this gives up to 28% better performance:
#semscale 10 | grep "interleave 2"
- before:
Cpus 1, interleave 2 delay 0: 36109234 in 10 secs
Cpus 2, interleave 2 delay 0: 55276317 in 10 secs
Cpus 3, interleave 2 delay 0: 62411025 in 10 secs
Cpus 4, interleave 2 delay 0: 81963928 in 10 secs
-after:
Cpus 1, interleave 2 delay 0: 35527306 in 10 secs
Cpus 2, interleave 2 delay 0: 70922909 in 10 secs <<< + 28%
Cpus 3, interleave 2 delay 0: 80518538 in 10 secs
Cpus 4, interleave 2 delay 0: 89115148 in 10 secs <<< + 8.7%
i3, with 2 cores and with hyperthreading enabled. Interleave 2 in order
use first the full cores. HT partially hides the delay from cacheline
trashing, thus the improvement is "only" 8.7% if 4 threads are running.
Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Davidlohr Bueso <davidlohr.bueso@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
ipc/sem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -96,7 +96,7 @@ struct sem {
int sempid; /* pid of last operation */
spinlock_t lock; /* spinlock for fine-grained semtimedop */
struct list_head sem_pending; /* pending single-sop operations */
-};
+} ____cacheline_aligned_in_smp;
/* One queue for each sleeping process in the system. */
struct sem_queue {
--
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