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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>
This commit is contained in:
Li Zefan 2008-04-29 01:00:11 -07:00 committed by Linus Torvalds
parent 08ce5f16ee
commit 472b1053f3
2 changed files with 53 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/cgroup.h
View File

@ -155,6 +155,12 @@ struct css_set {
*/
struct list_head list;
/*
* List running through all cgroup groups in the same hash
* slot. Protected by css_set_lock
*/
struct hlist_node hlist;
/*
* List running through all tasks using this cgroup
* group. Protected by css_set_lock
@ -174,7 +180,6 @@ struct css_set {
* during subsystem registration (at boot time).
*/
struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
};
/*

59
kernel/cgroup.c
View File

@ -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 struct cg_cgroup_link init_css_set_link;
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 int use_task_css_set_links;
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 @@ static inline void put_css_set_taskexit(struct css_set *cg)
/*
* 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 @@ static struct css_set *find_existing_css_set(
{
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 @@ static struct css_set *find_existing_css_set(
}
}
/* 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 @@ static struct css_set *find_css_set(
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 @@ static struct css_set *find_css_set(
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 @@ static struct css_set *find_css_set(
/* 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 @@ int __init cgroup_init_early(void)
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 @@ int __init cgroup_init_early(void)
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 __init cgroup_init(void)
{
int err;
int i;
struct hlist_head *hhead;
err = bdi_init(&cgroup_backing_dev_info);
if (err)
@ -2560,6 +2591,10 @@ int __init cgroup_init(void)
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;