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Message-ID: <6599ad830804020323q2509d242g156a595b89f63843@mail.gmail.com>
Date: Wed, 2 Apr 2008 03:23:59 -0700
From: "Paul Menage" <menage@...gle.com>
To: "Li Zefan" <lizf@...fujitsu.com>
Cc: "Andrew Morton" <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
containers@...ts.linux-foundation.org
Subject: Re: [PATCH -mm 1/3] cgroup: use a hash table for css_set finding
On Tue, Apr 1, 2008 at 7:16 PM, Li Zefan <lizf@...fujitsu.com> wrote:
> 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 benmarks has 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@...fujitsu.com>
Reviewed-by: Paul Menage <menage@...gle.com>
This looks good, thanks.
> ---
> include/linux/cgroup.h | 7 +++++-
> kernel/cgroup.c | 58 ++++++++++++++++++++++++++++++++++++++----------
> 2 files changed, 52 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 785a01c..c15c5e0 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -156,6 +156,12 @@ 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];
> -
> };
>
> /*
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index e8e8ec4..78e5bde 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 +194,26 @@ 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];
> +
> + 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 +240,7 @@ 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 +306,7 @@ 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 +323,9 @@ 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 +342,13 @@ 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 +410,8 @@ 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 +436,7 @@ 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 +479,11 @@ 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;
> @@ -2499,6 +2524,7 @@ 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);
> @@ -2511,6 +2537,9 @@ 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];
>
> @@ -2540,6 +2569,7 @@ int __init cgroup_init(void)
> {
> int err;
> int i;
> + struct hlist_head *hhead;
>
> err = bdi_init(&cgroup_backing_dev_info);
> if (err)
> @@ -2551,6 +2581,10 @@ 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;
> --
> 1.5.4.rc3
>
--
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