From 45333d5a31296d0af886d94f1d08f128231cab8e Mon Sep 17 00:00:00 2001 From: Aaron Carroll Date: Tue, 26 Aug 2008 15:52:36 +0200 Subject: [PATCH] cfq-iosched: fix queue depth detection CFQ's detection of queueing devices assumes a non-queuing device and detects if the queue depth reaches a certain threshold. Under some workloads (e.g. synchronous reads), CFQ effectively forces a unit queue depth, thus defeating the detection logic. This leads to poor performance on queuing hardware, since the idle window remains enabled. This patch inverts the sense of the logic: assume a queuing-capable device, and detect if the depth does not exceed the threshold. Signed-off-by: Aaron Carroll Signed-off-by: Jens Axboe --- block/cfq-iosched.c | 47 ++++++++++++++++++++++++++++++++++++--------- 1 file changed, 38 insertions(+), 9 deletions(-) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 5f6fd287c185..494b6fdcb183 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -39,6 +39,7 @@ static int cfq_slice_idle = HZ / 125; #define CFQ_MIN_TT (2) #define CFQ_SLICE_SCALE (5) +#define CFQ_HW_QUEUE_MIN (5) #define RQ_CIC(rq) \ ((struct cfq_io_context *) (rq)->elevator_private) @@ -86,7 +87,14 @@ struct cfq_data { int rq_in_driver; int sync_flight; + + /* + * queue-depth detection + */ + int rq_queued; int hw_tag; + int hw_tag_samples; + int rq_in_driver_peak; /* * idle window management @@ -654,15 +662,6 @@ static void cfq_activate_request(struct request_queue *q, struct request *rq) cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d", cfqd->rq_in_driver); - /* - * If the depth is larger 1, it really could be queueing. But lets - * make the mark a little higher - idling could still be good for - * low queueing, and a low queueing number could also just indicate - * a SCSI mid layer like behaviour where limit+1 is often seen. - */ - if (!cfqd->hw_tag && cfqd->rq_in_driver > 4) - cfqd->hw_tag = 1; - cfqd->last_position = rq->hard_sector + rq->hard_nr_sectors; } @@ -686,6 +685,7 @@ static void cfq_remove_request(struct request *rq) list_del_init(&rq->queuelist); cfq_del_rq_rb(rq); + cfqq->cfqd->rq_queued--; if (rq_is_meta(rq)) { WARN_ON(!cfqq->meta_pending); cfqq->meta_pending--; @@ -1833,6 +1833,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq, { struct cfq_io_context *cic = RQ_CIC(rq); + cfqd->rq_queued++; if (rq_is_meta(rq)) cfqq->meta_pending++; @@ -1880,6 +1881,31 @@ static void cfq_insert_request(struct request_queue *q, struct request *rq) cfq_rq_enqueued(cfqd, cfqq, rq); } +/* + * Update hw_tag based on peak queue depth over 50 samples under + * sufficient load. + */ +static void cfq_update_hw_tag(struct cfq_data *cfqd) +{ + if (cfqd->rq_in_driver > cfqd->rq_in_driver_peak) + cfqd->rq_in_driver_peak = cfqd->rq_in_driver; + + if (cfqd->rq_queued <= CFQ_HW_QUEUE_MIN && + cfqd->rq_in_driver <= CFQ_HW_QUEUE_MIN) + return; + + if (cfqd->hw_tag_samples++ < 50) + return; + + if (cfqd->rq_in_driver_peak >= CFQ_HW_QUEUE_MIN) + cfqd->hw_tag = 1; + else + cfqd->hw_tag = 0; + + cfqd->hw_tag_samples = 0; + cfqd->rq_in_driver_peak = 0; +} + static void cfq_completed_request(struct request_queue *q, struct request *rq) { struct cfq_queue *cfqq = RQ_CFQQ(rq); @@ -1890,6 +1916,8 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq) now = jiffies; cfq_log_cfqq(cfqd, cfqq, "complete"); + cfq_update_hw_tag(cfqd); + WARN_ON(!cfqd->rq_in_driver); WARN_ON(!cfqq->dispatched); cfqd->rq_in_driver--; @@ -2200,6 +2228,7 @@ static void *cfq_init_queue(struct request_queue *q) cfqd->cfq_slice[1] = cfq_slice_sync; cfqd->cfq_slice_async_rq = cfq_slice_async_rq; cfqd->cfq_slice_idle = cfq_slice_idle; + cfqd->hw_tag = 1; return cfqd; } -- 2.20.1