From f5c936c0f267ec58641451cf8b8d39b4c207ee4d Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Mon, 8 Jul 2013 16:01:22 -0700 Subject: [PATCH] ipc/sem.c: cacheline align the semaphore structures 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 Cc: Rik van Riel Cc: Davidlohr Bueso Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/sem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/ipc/sem.c b/ipc/sem.c index d3ad3573bc6f..8498b67a3b62 100644 --- 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 { -- 2.30.2