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Subject[PATCH] cfq-iosched: requests "in flight" vs "in driver" clarification
Date
Counters for requests "in flight" and "in driver" are used asymmetrically
in cfq_may_dispatch, and have slightly different meaning.
We split the rq_in_flight counter (was sync_flight) to count both sync
and async requests, in order to use this one, which is more accurate in
some corner cases.
The rq_in_driver counter is coalesced, since individual sync/async counts
are not used any more.

Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
---
block/cfq-iosched.c | 44 ++++++++++++++++++--------------------------
1 files changed, 18 insertions(+), 26 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 10eb286..eed649c 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -223,8 +223,8 @@ struct cfq_data {

unsigned int busy_queues;

- int rq_in_driver[2];
- int sync_flight;
+ int rq_in_driver;
+ int rq_in_flight[2];

/*
* queue-depth detection
@@ -417,11 +417,6 @@ static struct cfq_queue *cfq_get_queue(struct cfq_data *, bool,
static struct cfq_io_context *cfq_cic_lookup(struct cfq_data *,
struct io_context *);

-static inline int rq_in_driver(struct cfq_data *cfqd)
-{
- return cfqd->rq_in_driver[0] + cfqd->rq_in_driver[1];
-}
-
static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_context *cic,
bool is_sync)
{
@@ -1415,9 +1410,9 @@ static void cfq_activate_request(struct request_queue *q, struct request *rq)
{
struct cfq_data *cfqd = q->elevator->elevator_data;

- cfqd->rq_in_driver[rq_is_sync(rq)]++;
+ cfqd->rq_in_driver++;
cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",
- rq_in_driver(cfqd));
+ cfqd->rq_in_driver);

cfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
}
@@ -1425,12 +1420,11 @@ static void cfq_activate_request(struct request_queue *q, struct request *rq)
static void cfq_deactivate_request(struct request_queue *q, struct request *rq)
{
struct cfq_data *cfqd = q->elevator->elevator_data;
- const int sync = rq_is_sync(rq);

- WARN_ON(!cfqd->rq_in_driver[sync]);
- cfqd->rq_in_driver[sync]--;
+ WARN_ON(!cfqd->rq_in_driver);
+ cfqd->rq_in_driver--;
cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "deactivate rq, drv=%d",
- rq_in_driver(cfqd));
+ cfqd->rq_in_driver);
}

static void cfq_remove_request(struct request *rq)
@@ -1873,8 +1867,7 @@ static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
cfqq->dispatched++;
elv_dispatch_sort(q, rq);

- if (cfq_cfqq_sync(cfqq))
- cfqd->sync_flight++;
+ cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]++;
cfqq->nr_sectors += blk_rq_sectors(rq);
}

@@ -2221,13 +2214,13 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
/*
* Drain async requests before we start sync IO
*/
- if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_driver[BLK_RW_ASYNC])
+ if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_flight[BLK_RW_ASYNC])
return false;

/*
* If this is an async queue and we have sync IO in flight, let it wait
*/
- if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq))
+ if (cfqd->rq_in_flight[BLK_RW_SYNC] && !cfq_cfqq_sync(cfqq))
return false;

max_dispatch = cfqd->cfq_quantum;
@@ -3210,14 +3203,14 @@ static void cfq_update_hw_tag(struct cfq_data *cfqd)
{
struct cfq_queue *cfqq = cfqd->active_queue;

- if (rq_in_driver(cfqd) > cfqd->hw_tag_est_depth)
- cfqd->hw_tag_est_depth = rq_in_driver(cfqd);
+ if (cfqd->rq_in_driver > cfqd->hw_tag_est_depth)
+ cfqd->hw_tag_est_depth = cfqd->rq_in_driver;

if (cfqd->hw_tag == 1)
return;

if (cfqd->rq_queued <= CFQ_HW_QUEUE_MIN &&
- rq_in_driver(cfqd) <= CFQ_HW_QUEUE_MIN)
+ cfqd->rq_in_driver <= CFQ_HW_QUEUE_MIN)
return;

/*
@@ -3227,7 +3220,7 @@ static void cfq_update_hw_tag(struct cfq_data *cfqd)
*/
if (cfqq && cfq_cfqq_idle_window(cfqq) &&
cfqq->dispatched + cfqq->queued[0] + cfqq->queued[1] <
- CFQ_HW_QUEUE_MIN && rq_in_driver(cfqd) < CFQ_HW_QUEUE_MIN)
+ CFQ_HW_QUEUE_MIN && cfqd->rq_in_driver < CFQ_HW_QUEUE_MIN)
return;

if (cfqd->hw_tag_samples++ < 50)
@@ -3280,13 +3273,12 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)

cfq_update_hw_tag(cfqd);

- WARN_ON(!cfqd->rq_in_driver[sync]);
+ WARN_ON(!cfqd->rq_in_driver);
WARN_ON(!cfqq->dispatched);
- cfqd->rq_in_driver[sync]--;
+ cfqd->rq_in_driver--;
cfqq->dispatched--;

- if (cfq_cfqq_sync(cfqq))
- cfqd->sync_flight--;
+ cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]--;

if (sync) {
RQ_CIC(rq)->last_end_request = now;
@@ -3340,7 +3332,7 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
}
}

- if (!rq_in_driver(cfqd))
+ if (!cfqd->rq_in_driver)
cfq_schedule_dispatch(cfqd);
}

--
1.6.4.4


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