From 5d2ee7122c73be6a3b6bfe90d237e8aed737cfaa Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Thu, 29 Nov 2018 17:36:41 -0700 Subject: sbitmap: optimize wakeup check Even if we have no waiters on any of the sbitmap_queue wait states, we still have to loop every entry to check. We do this for every IO, so the cost adds up. Shift a bit of the cost to the slow path, when we actually have waiters. Wrap prepare_to_wait_exclusive() and finish_wait(), so we can maintain an internal count of how many are currently active. Then we can simply check this count in sbq_wake_ptr() and not have to loop if we don't have any sleepers. Convert the two users of sbitmap with waiting, blk-mq-tag and iSCSI. Reviewed-by: Omar Sandoval Signed-off-by: Jens Axboe --- lib/sbitmap.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) (limited to 'lib/sbitmap.c') diff --git a/lib/sbitmap.c b/lib/sbitmap.c index f99382e59314..a89fbe7cf6ca 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -394,6 +394,7 @@ int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth, sbq->min_shallow_depth = UINT_MAX; sbq->wake_batch = sbq_calc_wake_batch(sbq, depth); atomic_set(&sbq->wake_index, 0); + atomic_set(&sbq->ws_active, 0); sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node); if (!sbq->ws) { @@ -509,6 +510,9 @@ static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq) { int i, wake_index; + if (!atomic_read(&sbq->ws_active)) + return NULL; + wake_index = atomic_read(&sbq->wake_index); for (i = 0; i < SBQ_WAIT_QUEUES; i++) { struct sbq_wait_state *ws = &sbq->ws[wake_index]; @@ -634,6 +638,7 @@ void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m) seq_printf(m, "wake_batch=%u\n", sbq->wake_batch); seq_printf(m, "wake_index=%d\n", atomic_read(&sbq->wake_index)); + seq_printf(m, "ws_active=%d\n", atomic_read(&sbq->ws_active)); seq_puts(m, "ws={\n"); for (i = 0; i < SBQ_WAIT_QUEUES; i++) { @@ -649,3 +654,26 @@ void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m) seq_printf(m, "min_shallow_depth=%u\n", sbq->min_shallow_depth); } EXPORT_SYMBOL_GPL(sbitmap_queue_show); + +void sbitmap_prepare_to_wait(struct sbitmap_queue *sbq, + struct sbq_wait_state *ws, + struct sbq_wait *sbq_wait, int state) +{ + if (!sbq_wait->accounted) { + atomic_inc(&sbq->ws_active); + sbq_wait->accounted = 1; + } + prepare_to_wait_exclusive(&ws->wait, &sbq_wait->wait, state); +} +EXPORT_SYMBOL_GPL(sbitmap_prepare_to_wait); + +void sbitmap_finish_wait(struct sbitmap_queue *sbq, struct sbq_wait_state *ws, + struct sbq_wait *sbq_wait) +{ + finish_wait(&ws->wait, &sbq_wait->wait); + if (sbq_wait->accounted) { + atomic_dec(&sbq->ws_active); + sbq_wait->accounted = 0; + } +} +EXPORT_SYMBOL_GPL(sbitmap_finish_wait); -- cgit