cgroups: use a hash table for css_set finding
When we attach a process to a different cgroup, the css_set linked-list will
be run through to find a suitable existing css_set to use. This patch
implements a hash table for better performance.
The following benchmarks have been tested:
For N in 1, 5, 10, 50, 100, 500, 1000, create N cgroups with one sleeping
task in each, and then move an additional task through each cgroup in
turn.
Here is a test result:
N Loop orig - Time(s) hash - Time(s)
----------------------------------------------
1 10000 1.201231728 1.196311177
5 2000 1.065743872 1.040566424
10 1000 0.991054735 0.986876440
50 200 0.976554203 0.969608733
100 100 0.998504680 0.969218270
500 20 1.157347764 0.962602963
1000 10 1.619521852 1.085140172
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Reviewed-by: Paul Menage <menage@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7c8cc51..c447c29 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -44,6 +44,7 @@
#include <linux/kmod.h>
#include <linux/delayacct.h>
#include <linux/cgroupstats.h>
+#include <linux/hash.h>
#include <asm/atomic.h>
@@ -193,6 +194,27 @@
static DEFINE_RWLOCK(css_set_lock);
static int css_set_count;
+/* hash table for cgroup groups. This improves the performance to
+ * find an existing css_set */
+#define CSS_SET_HASH_BITS 7
+#define CSS_SET_TABLE_SIZE (1 << CSS_SET_HASH_BITS)
+static struct hlist_head css_set_table[CSS_SET_TABLE_SIZE];
+
+static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])
+{
+ int i;
+ int index;
+ unsigned long tmp = 0UL;
+
+ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
+ tmp += (unsigned long)css[i];
+ tmp = (tmp >> 16) ^ tmp;
+
+ index = hash_long(tmp, CSS_SET_HASH_BITS);
+
+ return &css_set_table[index];
+}
+
/* We don't maintain the lists running through each css_set to its
* task until after the first call to cgroup_iter_start(). This
* reduces the fork()/exit() overhead for people who have cgroups
@@ -219,6 +241,7 @@
static void unlink_css_set(struct css_set *cg)
{
write_lock(&css_set_lock);
+ hlist_del(&cg->hlist);
list_del(&cg->list);
css_set_count--;
while (!list_empty(&cg->cg_links)) {
@@ -284,9 +307,7 @@
/*
* find_existing_css_set() is a helper for
* find_css_set(), and checks to see whether an existing
- * css_set is suitable. This currently walks a linked-list for
- * simplicity; a later patch will use a hash table for better
- * performance
+ * css_set is suitable.
*
* oldcg: the cgroup group that we're using before the cgroup
* transition
@@ -303,7 +324,9 @@
{
int i;
struct cgroupfs_root *root = cgrp->root;
- struct list_head *l = &init_css_set.list;
+ struct hlist_head *hhead;
+ struct hlist_node *node;
+ struct css_set *cg;
/* Built the set of subsystem state objects that we want to
* see in the new css_set */
@@ -320,18 +343,13 @@
}
}
- /* Look through existing cgroup groups to find one to reuse */
- do {
- struct css_set *cg =
- list_entry(l, struct css_set, list);
-
+ hhead = css_set_hash(template);
+ hlist_for_each_entry(cg, node, hhead, hlist) {
if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) {
/* All subsystems matched */
return cg;
}
- /* Try the next cgroup group */
- l = l->next;
- } while (l != &init_css_set.list);
+ }
/* No existing cgroup group matched */
return NULL;
@@ -393,6 +411,8 @@
struct list_head tmp_cg_links;
struct cg_cgroup_link *link;
+ struct hlist_head *hhead;
+
/* First see if we already have a cgroup group that matches
* the desired set */
write_lock(&css_set_lock);
@@ -417,6 +437,7 @@
kref_init(&res->ref);
INIT_LIST_HEAD(&res->cg_links);
INIT_LIST_HEAD(&res->tasks);
+ INIT_HLIST_NODE(&res->hlist);
/* Copy the set of subsystem state objects generated in
* find_existing_css_set() */
@@ -459,6 +480,11 @@
/* Link this cgroup group into the list */
list_add(&res->list, &init_css_set.list);
css_set_count++;
+
+ /* Add this cgroup group to the hash table */
+ hhead = css_set_hash(res->subsys);
+ hlist_add_head(&res->hlist, hhead);
+
write_unlock(&css_set_lock);
return res;
@@ -2508,6 +2534,7 @@
INIT_LIST_HEAD(&init_css_set.list);
INIT_LIST_HEAD(&init_css_set.cg_links);
INIT_LIST_HEAD(&init_css_set.tasks);
+ INIT_HLIST_NODE(&init_css_set.hlist);
css_set_count = 1;
init_cgroup_root(&rootnode);
list_add(&rootnode.root_list, &roots);
@@ -2520,6 +2547,9 @@
list_add(&init_css_set_link.cg_link_list,
&init_css_set.cg_links);
+ for (i = 0; i < CSS_SET_TABLE_SIZE; i++)
+ INIT_HLIST_HEAD(&css_set_table[i]);
+
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
@@ -2549,6 +2579,7 @@
{
int err;
int i;
+ struct hlist_head *hhead;
err = bdi_init(&cgroup_backing_dev_info);
if (err)
@@ -2560,6 +2591,10 @@
cgroup_init_subsys(ss);
}
+ /* Add init_css_set to the hash table */
+ hhead = css_set_hash(init_css_set.subsys);
+ hlist_add_head(&init_css_set.hlist, hhead);
+
err = register_filesystem(&cgroup_fs_type);
if (err < 0)
goto out;