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Message-ID: <1293072335.10593.22.camel@sli10-conroe>
Date: Thu, 23 Dec 2010 10:45:35 +0800
From: Shaohua Li <shaohua.li@...el.com>
To: lkml <linux-kernel@...r.kernel.org>
Cc: Jens Axboe <jaxboe@...ionio.com>, vgoyal@...hat.com,
jmoyer@...hat.com
Subject: [PATCH 2/2]block cfq: don't use atomic_t for cfq_group
cfq_group->ref is used with queue_lock hold, the only exception is
cfq_set_request, which looks like a bug to me, so ref doesn't need
to be an atomic and atomic operation is slower.
Signed-off-by: Shaohua Li <shaohua.li@...el.com>
---
block/cfq-iosched.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
Index: linux/block/cfq-iosched.c
===================================================================
--- linux.orig/block/cfq-iosched.c 2010-12-23 10:22:21.000000000 +0800
+++ linux/block/cfq-iosched.c 2010-12-23 10:23:03.000000000 +0800
@@ -209,7 +209,7 @@ struct cfq_group {
struct blkio_group blkg;
#ifdef CONFIG_CFQ_GROUP_IOSCHED
struct hlist_node cfqd_node;
- atomic_t ref;
+ int ref;
#endif
/* number of requests that are on the dispatch list or inside driver */
int dispatched;
@@ -1026,7 +1026,7 @@ cfq_find_alloc_cfqg(struct cfq_data *cfq
* elevator which will be dropped by either elevator exit
* or cgroup deletion path depending on who is exiting first.
*/
- atomic_set(&cfqg->ref, 1);
+ cfqg->ref = 1;
/*
* Add group onto cgroup list. It might happen that bdi->dev is
@@ -1071,7 +1071,7 @@ static struct cfq_group *cfq_get_cfqg(st
static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
{
- atomic_inc(&cfqg->ref);
+ cfqg->ref++;
return cfqg;
}
@@ -1083,7 +1083,7 @@ static void cfq_link_cfqq_cfqg(struct cf
cfqq->cfqg = cfqg;
/* cfqq reference on cfqg */
- atomic_inc(&cfqq->cfqg->ref);
+ cfqq->cfqg->ref++;
}
static void cfq_put_cfqg(struct cfq_group *cfqg)
@@ -1091,8 +1091,9 @@ static void cfq_put_cfqg(struct cfq_grou
struct cfq_rb_root *st;
int i, j;
- BUG_ON(atomic_read(&cfqg->ref) <= 0);
- if (!atomic_dec_and_test(&cfqg->ref))
+ BUG_ON(cfqg->ref <= 0);
+ cfqg->ref--;
+ if (cfqg->ref)
return;
for_each_cfqg_st(cfqg, i, j, st)
BUG_ON(!RB_EMPTY_ROOT(&st->rb) || st->active != NULL);
@@ -1200,7 +1201,7 @@ static void cfq_service_tree_add(struct
cfq_group_service_tree_del(cfqd, cfqq->cfqg);
cfqq->orig_cfqg = cfqq->cfqg;
cfqq->cfqg = &cfqd->root_group;
- atomic_inc(&cfqd->root_group.ref);
+ cfqd->root_group.ref++;
group_changed = 1;
} else if (!cfqd->cfq_group_isolation
&& cfqq_type(cfqq) == SYNC_WORKLOAD && cfqq->orig_cfqg) {
@@ -3645,6 +3646,7 @@ cfq_set_request(struct request_queue *q,
const bool is_sync = rq_is_sync(rq);
struct cfq_queue *cfqq;
unsigned long flags;
+ struct cfq_group *cfqg;
might_sleep_if(gfp_mask & __GFP_WAIT);
@@ -3683,12 +3685,13 @@ new_queue:
cfqq->allocated[rw]++;
cfqq->ref++;
+ cfqg = cfq_ref_get_cfqg(cfqq->cfqg);
spin_unlock_irqrestore(q->queue_lock, flags);
rq->elevator_private = cic;
rq->elevator_private2 = cfqq;
- rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg);
+ rq->elevator_private3 = cfqg;
return 0;
queue_fail:
@@ -3886,7 +3889,7 @@ static void *cfq_init_queue(struct reque
* Take a reference to root group which we never drop. This is just
* to make sure that cfq_put_cfqg() does not try to kfree root group
*/
- atomic_set(&cfqg->ref, 1);
+ cfqg->ref = 1;
rcu_read_lock();
cfq_blkiocg_add_blkio_group(&blkio_root_cgroup, &cfqg->blkg,
(void *)cfqd, 0);
--
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