2019-10-07 21:20:03

by Pavel Begunkov

Subject: [PATCH] blk-stat: Optimise blk_stat_add()

From: Pavel Begunkov <[email protected]>

blk_stat_add() calls {get,put}_cpu_ptr() in a loop, which entails
overhead of disabling/enabling preemption. The loop is under RCU
(i.e.short) anyway, so do get_cpu() in advance.

Signed-off-by: Pavel Begunkov <[email protected]>
---
block/blk-stat.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/blk-stat.c b/block/blk-stat.c
index d892ad2cb938..4239954b0bce 100644
--- a/block/blk-stat.c
+++ b/block/blk-stat.c
@@ -75,7 +75,7 @@ void blk_stat_add(struct request *rq, u64 now)
struct request_queue *q = rq->q;
struct blk_stat_callback *cb;
struct blk_rq_stat_staging *stat;
- int bucket;
+ int bucket, cpu;
u64 value;

value = (now >= rq->io_start_time_ns) ? now - rq->io_start_time_ns : 0;
@@ -83,6 +83,7 @@ void blk_stat_add(struct request *rq, u64 now)
blk_throtl_stat_add(rq, value);

rcu_read_lock();
+ cpu = get_cpu();
list_for_each_entry_rcu(cb, &q->stats->callbacks, list) {
if (!blk_stat_is_active(cb))
continue;
@@ -91,10 +92,10 @@ void blk_stat_add(struct request *rq, u64 now)
if (bucket < 0)
continue;

- stat = &get_cpu_ptr(cb->cpu_stat)[bucket];
+ stat = &per_cpu_ptr(cb->cpu_stat, cpu)[bucket];
blk_rq_stat_add(stat, value);
- put_cpu_ptr(cb->cpu_stat);
}
+ put_cpu();
rcu_read_unlock();
}

--
2.23.0

2019-10-08 03:20:59

by Jens Axboe

Subject: Re: [PATCH] blk-stat: Optimise blk_stat_add()

On 10/7/19 3:16 PM, Pavel Begunkov (Silence) wrote:
> From: Pavel Begunkov <[email protected]>
>
> blk_stat_add() calls {get,put}_cpu_ptr() in a loop, which entails
> overhead of disabling/enabling preemption. The loop is under RCU
> (i.e.short) anyway, so do get_cpu() in advance.

Looks good, applied for 5.5.

--
Jens Axboe