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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 <aaronc@gelato.unsw.edu.au>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Aaron Carroll 2008-08-26 15:52:36 +02:00 committed by Jens Axboe
parent 605401618c
commit 45333d5a31
1 changed files with 38 additions and 9 deletions
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47
block/cfq-iosched.c
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@ -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;
}