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Subject[PATCH V2 03/22] block, cfq: remove deep seek queues logic
Date
From: Arianna Avanzini <avanzini.arianna@gmail.com>

CFQ implements a heuristic to identify seeky queues experiencing large
queue depths (>= 4), and let them idle despite their seekiness. This
mechanism has no match in BFQ, where idling decisions are taken
according to a unified global strategy. In this strategy, all actions
are aimed at boosting the throughput, except for when
throughput-boosting actions would jeopardize throughput-distribution
and latency guarantees. Full details in the commits turning CFQ into
BFQ.

Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
---
block/cfq-iosched.c | 20 +++-----------------
1 file changed, 3 insertions(+), 17 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 1ab8898..04d2298 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -411,7 +411,6 @@ enum cfqq_state_flags {
CFQ_CFQQ_FLAG_prio_changed, /* task priority has changed */
CFQ_CFQQ_FLAG_slice_new, /* no requests dispatched in slice */
CFQ_CFQQ_FLAG_sync, /* synchronous queue */
- CFQ_CFQQ_FLAG_deep, /* sync cfqq experienced large depth */
CFQ_CFQQ_FLAG_wait_busy, /* Waiting for next request */
};

@@ -438,7 +437,6 @@ CFQ_CFQQ_FNS(idle_window);
CFQ_CFQQ_FNS(prio_changed);
CFQ_CFQQ_FNS(slice_new);
CFQ_CFQQ_FNS(sync);
-CFQ_CFQQ_FNS(deep);
CFQ_CFQQ_FNS(wait_busy);
#undef CFQ_CFQQ_FNS

@@ -3060,15 +3058,12 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
}

/*
- * This is a deep seek queue, but the device is much faster than
- * the queue can deliver, don't idle
+ * The device is much faster than the queue can deliver: don't idle
**/
if (CFQQ_SEEKY(cfqq) && cfq_cfqq_idle_window(cfqq) &&
(cfq_cfqq_slice_new(cfqq) ||
- (cfqq->slice_end - now > now - cfqq->slice_start))) {
- cfq_clear_cfqq_deep(cfqq);
+ (cfqq->slice_end - now > now - cfqq->slice_start)))
cfq_clear_cfqq_idle_window(cfqq);
- }

if (cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
cfqq = NULL;
@@ -3649,14 +3644,10 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,

enable_idle = old_idle = cfq_cfqq_idle_window(cfqq);

- if (cfqq->queued[0] + cfqq->queued[1] >= 4)
- cfq_mark_cfqq_deep(cfqq);
-
if (cfqq->next_rq && (cfqq->next_rq->cmd_flags & REQ_NOIDLE))
enable_idle = 0;
else if (!atomic_read(&cic->icq.ioc->active_ref) ||
- !cfqd->cfq_slice_idle ||
- (!cfq_cfqq_deep(cfqq) && CFQQ_SEEKY(cfqq)))
+ !cfqd->cfq_slice_idle || CFQQ_SEEKY(cfqq))
enable_idle = 0;
else if (sample_valid(cic->ttime.ttime_samples)) {
if (cic->ttime.ttime_mean > cfqd->cfq_slice_idle)
@@ -4185,11 +4176,6 @@ static enum hrtimer_restart cfq_idle_slice_timer(struct hrtimer *timer)
*/
if (!RB_EMPTY_ROOT(&cfqq->sort_list))
goto out_kick;
-
- /*
- * Queue depth flag is reset only when the idle didn't succeed
- */
- cfq_clear_cfqq_deep(cfqq);
}
expire:
cfq_slice_expired(cfqd, timed_out);
--
1.9.1
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