From 804b3c28a4e4fa1c224571bf76edb534b9c4b1ed Mon Sep 17 00:00:00 2001 From: Paul Menage 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 e267e62827bb..e4e8e117d27d 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 0066092de19a..492215d67fa5 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) {