The patch titled
cfq-iosched: fix queue depth detection
has been added to the -mm tree. Its filename is
cfq-iosched-fix-queue-depth-detection.patch
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------------------------------------------------------
Subject: cfq-iosched: fix queue depth detection
From: Aaron Carroll <aaronc@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
block/cfq-iosched.c | 47 +++++++++++++++++++++++++++++++++---------
1 file changed, 38 insertions(+), 9 deletions(-)
diff -puN block/cfq-iosched.c~cfq-iosched-fix-queue-depth-detection block/cfq-iosched.c
--- a/block/cfq-iosched.c~cfq-iosched-fix-queue-depth-detection
+++ a/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
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 re
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, s
{
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 re
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
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 reque
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;
}
_
Patches currently in -mm which might be from aaronc@xxxxxxxxxxxxxxxxxx are
linux-next.patch
cfq-iosched-fix-queue-depth-detection.patch
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