From 804b3c28a4e4fa1c224571bf76edb534b9c4b1ed Mon Sep 17 00:00:00 2001
From: Paul Menage <menage@google.com>
Date: Thu, 29 Jan 2009 14:25:21 -0800
Subject: [PATCH] cgroups: add cpu_relax() calls in css_tryget() and
cgroup_clear_css_refs()
css_tryget() and cgroup_clear_css_refs() contain polling loops; these
loops should have cpu_relax calls in them to reduce cross-cache traffic.
Signed-off-by: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
include/linux/cgroup.h | 1 +
kernel/cgroup.c | 7 +++++--
2 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e267e62827bbc..e4e8e117d27d9 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -99,6 +99,7 @@ static inline bool css_tryget(struct cgroup_subsys_state *css)
while (!atomic_inc_not_zero(&css->refcnt)) {
if (test_bit(CSS_REMOVED, &css->flags))
return false;
+ cpu_relax();
}
return true;
}
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0066092de19a7..492215d67fa5c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2509,7 +2509,7 @@ static int cgroup_clear_css_refs(struct cgroup *cgrp)
for_each_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
int refcnt;
- do {
+ while (1) {
/* We can only remove a CSS with a refcnt==1 */
refcnt = atomic_read(&css->refcnt);
if (refcnt > 1) {
@@ -2523,7 +2523,10 @@ static int cgroup_clear_css_refs(struct cgroup *cgrp)
* css_tryget() to spin until we set the
* CSS_REMOVED bits or abort
*/
- } while (atomic_cmpxchg(&css->refcnt, refcnt, 0) != refcnt);
+ if (atomic_cmpxchg(&css->refcnt, refcnt, 0) == refcnt)
+ break;
+ cpu_relax();
+ }
}
done:
for_each_subsys(cgrp->root, ss) {
--
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