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block, bfq: move debug blkio stats behind CONFIG_DEBUG_BLK_CGROUP

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BFQ currently creates, and updates, its own instance of the whole
set of blkio statistics that cfq creates. Yet, from the comments
of Tejun Heo in [1], it turned out that most of these statistics
are meant/useful only for debugging. This commit makes BFQ create
the latter, debugging statistics only if the option
CONFIG_DEBUG_BLK_CGROUP is set.

By doing so, this commit also enables BFQ to enjoy a high perfomance
boost. The reason is that, if CONFIG_DEBUG_BLK_CGROUP is not set, then
BFQ has to update far fewer statistics, and, in particular, not the
heaviest to update.  To give an idea of the benefits, if
CONFIG_DEBUG_BLK_CGROUP is not set, then, on an Intel i7-4850HQ, and
with 8 threads doing random I/O in parallel on null_blk (configured
with 0 latency), the throughput of BFQ grows from 310 to 400 KIOPS
(+30%). We have measured similar or even much higher boosts with other
CPUs: e.g., +45% with an ARM CortexTM-A53 Octa-core. Our results have
been obtained and can be reproduced very easily with the script in [1].

[1] https://www.spinics.net/lists/linux-block/msg18943.html

Suggested-by: Tejun Heo <[email protected]>
Suggested-by: Ulf Hansson <[email protected]>
Tested-by: Lee Tibbert <[email protected]>
Tested-by: Oleksandr Natalenko <[email protected]>
Signed-off-by: Luca Miccio <[email protected]>
Signed-off-by: Paolo Valente <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Luca Miccio 2017-11-13 07:34:10 +01:00 • committed by Jens Axboe
commit a33801e8b4
4 changed files with 125 additions and 79 deletions
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14
block/bfq-iosched.c
View file

@ -3693,14 +3693,14 @@ static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
{
struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
struct request *rq;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
#if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
struct bfq_queue *in_serv_queue, *bfqq;
bool waiting_rq, idle_timer_disabled;
#endif
spin_lock_irq(&bfqd->lock);
#ifdef CONFIG_BFQ_GROUP_IOSCHED
#if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
in_serv_queue = bfqd->in_service_queue;
waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue);
@ -3714,7 +3714,7 @@ static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
#endif
spin_unlock_irq(&bfqd->lock);
#ifdef CONFIG_BFQ_GROUP_IOSCHED
#if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
bfqq = rq ? RQ_BFQQ(rq) : NULL;
if (!idle_timer_disabled && !bfqq)
return rq;
@ -4281,7 +4281,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
{
struct request_queue *q = hctx->queue;
struct bfq_data *bfqd = q->elevator->elevator_data;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
#if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
struct bfq_queue *bfqq = RQ_BFQQ(rq);
bool idle_timer_disabled = false;
unsigned int cmd_flags;
@ -4304,7 +4304,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
else
list_add_tail(&rq->queuelist, &bfqd->dispatch);
} else {
#ifdef CONFIG_BFQ_GROUP_IOSCHED
#if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
idle_timer_disabled = __bfq_insert_request(bfqd, rq);
/*
* Update bfqq, because, if a queue merge has occurred
@ -4323,7 +4323,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
}
}
#ifdef CONFIG_BFQ_GROUP_IOSCHED
#if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
/*
* Cache cmd_flags before releasing scheduler lock, because rq
* may disappear afterwards (for example, because of a request
@ -4333,7 +4333,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
#endif
spin_unlock_irq(&bfqd->lock);
#ifdef CONFIG_BFQ_GROUP_IOSCHED
#if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
if (!bfqq)
return;
/*