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

include/linux/cgroup.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

}

kernel/cgroup.c

+5 −2
Original line number Diff line number Diff line
@@ -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) {