Commit 804b3c28 authored by Paul Menage's avatar Paul Menage Committed by Linus Torvalds

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: default avatarPaul Menage <menage@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1404f065
...@@ -99,6 +99,7 @@ static inline bool css_tryget(struct cgroup_subsys_state *css) ...@@ -99,6 +99,7 @@ static inline bool css_tryget(struct cgroup_subsys_state *css)
while (!atomic_inc_not_zero(&css->refcnt)) { while (!atomic_inc_not_zero(&css->refcnt)) {
if (test_bit(CSS_REMOVED, &css->flags)) if (test_bit(CSS_REMOVED, &css->flags))
return false; return false;
cpu_relax();
} }
return true; return true;
} }
......
...@@ -2509,7 +2509,7 @@ static int cgroup_clear_css_refs(struct cgroup *cgrp) ...@@ -2509,7 +2509,7 @@ static int cgroup_clear_css_refs(struct cgroup *cgrp)
for_each_subsys(cgrp->root, ss) { for_each_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id]; struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
int refcnt; int refcnt;
do { while (1) {
/* We can only remove a CSS with a refcnt==1 */ /* We can only remove a CSS with a refcnt==1 */
refcnt = atomic_read(&css->refcnt); refcnt = atomic_read(&css->refcnt);
if (refcnt > 1) { if (refcnt > 1) {
...@@ -2523,7 +2523,10 @@ static int cgroup_clear_css_refs(struct cgroup *cgrp) ...@@ -2523,7 +2523,10 @@ static int cgroup_clear_css_refs(struct cgroup *cgrp)
* css_tryget() to spin until we set the * css_tryget() to spin until we set the
* CSS_REMOVED bits or abort * 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: done:
for_each_subsys(cgrp->root, ss) { for_each_subsys(cgrp->root, ss) {
......
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