The logic that decides whether to idle the device is scattered across
three functions. Almost all of the logic is in the function
bfq_bfqq_may_idle, but (1) part of the decision is made in
bfq_update_idle_window, and (2) the function bfq_bfqq_must_idle may
switch off idling regardless of the output of bfq_bfqq_may_idle. In
addition, both bfq_update_idle_window and bfq_bfqq_must_idle make
their decisions as a function of parameters that are used, for similar
purposes, also in bfq_bfqq_may_idle. This commit addresses these
issues by moving all the logic into bfq_bfqq_may_idle.
Signed-off-by: Paolo Valente <paolo.vale...@linaro.org>
---
block/bfq-iosched.c | 117 +++++++++++++++++++++++++++-------------------------
block/bfq-iosched.h | 12 +++---
2 files changed, 67 insertions(+), 62 deletions(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 436b6ca..ccdc9e6 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -128,7 +128,7 @@ BFQ_BFQQ_FNS(busy);
BFQ_BFQQ_FNS(wait_request);
BFQ_BFQQ_FNS(non_blocking_wait_rq);
BFQ_BFQQ_FNS(fifo_expire);
-BFQ_BFQQ_FNS(idle_window);
+BFQ_BFQQ_FNS(has_short_ttime);
BFQ_BFQQ_FNS(sync);
BFQ_BFQQ_FNS(IO_bound);
BFQ_BFQQ_FNS(in_large_burst);
@@ -731,10 +731,10 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct
bfq_data *bfqd,
unsigned int old_wr_coeff = bfqq->wr_coeff;
bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
- if (bic->saved_idle_window)
- bfq_mark_bfqq_idle_window(bfqq);
+ if (bic->saved_has_short_ttime)
+ bfq_mark_bfqq_has_short_ttime(bfqq);
else
- bfq_clear_bfqq_idle_window(bfqq);
+ bfq_clear_bfqq_has_short_ttime(bfqq);
if (bic->saved_IO_bound)
bfq_mark_bfqq_IO_bound(bfqq);
@@ -2012,7 +2012,7 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
return;
bic->saved_ttime = bfqq->ttime;
- bic->saved_idle_window = bfq_bfqq_idle_window(bfqq);
+ bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
@@ -3038,8 +3038,8 @@ void bfq_bfqq_expire(struct bfq_data *bfqd,
}
bfq_log_bfqq(bfqd, bfqq,
- "expire (%d, slow %d, num_disp %d, idle_win %d)", reason,
- slow, bfqq->dispatched, bfq_bfqq_idle_window(bfqq));
+ "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason,
+ slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq));
/*
* Increase, decrease or leave budget unchanged according to
@@ -3122,6 +3122,18 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
return true;
/*
+ * Idling is performed only if slice_idle > 0. In addition, we
+ * do not idle if
+ * (a) bfqq is async
+ * (b) bfqq is in the idle io prio class: in this case we do
+ * not idle because we want to minimize the bandwidth that
+ * queues in this class can steal to higher-priority queues
+ */
+ if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) ||
+ bfq_class_idle(bfqq))
+ return false;
+
+ /*
* The next variable takes into account the cases where idling
* boosts the throughput.
*
@@ -3142,7 +3154,7 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
*/
idling_boosts_thr = !bfqd->hw_tag ||
(!blk_queue_nonrot(bfqd->queue) && bfq_bfqq_IO_bound(bfqq) &&
- bfq_bfqq_idle_window(bfqq));
+ bfq_bfqq_has_short_ttime(bfqq));
/*
* The value of the next variable,
@@ -3313,16 +3325,13 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
asymmetric_scenario && !bfq_bfqq_in_large_burst(bfqq);
/*
- * We have now all the components we need to compute the return
- * value of the function, which is true only if both the following
- * conditions hold:
- * 1) bfqq is sync, because idling make sense only for sync queues;
- * 2) idling either boosts the throughput (without issues), or
- * is necessary to preserve service guarantees.
+ * We have now all the components we need to compute the
+ * return value of the function, which is true only if idling
+ * either boosts the throughput (without issues), or is
+ * necessary to preserve service guarantees.
*/
- return bfq_bfqq_sync(bfqq) &&
- (idling_boosts_thr_without_issues ||
- idling_needed_for_service_guarantees);
+ return idling_boosts_thr_without_issues ||
+ idling_needed_for_service_guarantees;
}
/*
@@ -3338,10 +3347,7 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
*/
static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
{
- struct bfq_data *bfqd = bfqq->bfqd;
-
- return RB_EMPTY_ROOT(&bfqq->sort_list) && bfqd->bfq_slice_idle != 0 &&
- bfq_bfqq_may_idle(bfqq);
+ return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_may_idle(bfqq);
}
/*
@@ -3783,7 +3789,6 @@ bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct
bfq_io_cq *bic)
case IOPRIO_CLASS_IDLE:
bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
bfqq->new_ioprio = 7;
- bfq_clear_bfqq_idle_window(bfqq);
break;
}
@@ -3843,8 +3848,14 @@ static void bfq_init_bfqq(struct bfq_data *bfqd, struct
bfq_queue *bfqq,
bfq_set_next_ioprio_data(bfqq, bic);
if (is_sync) {
+ /*
+ * No need to mark as has_short_ttime if in
+ * idle_class, because no device idling is performed
+ * for queues in idle class
+ */
if (!bfq_class_idle(bfqq))
- bfq_mark_bfqq_idle_window(bfqq);
+ /* tentatively mark as has_short_ttime */
+ bfq_mark_bfqq_has_short_ttime(bfqq);
bfq_mark_bfqq_sync(bfqq);
bfq_mark_bfqq_just_created(bfqq);
} else
@@ -3985,18 +3996,19 @@ bfq_update_io_seektime(struct bfq_data *bfqd, struct
bfq_queue *bfqq,
blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT);
}
-/*
- * Disable idle window if the process thinks too long or seeks so much that
- * it doesn't matter.
- */
-static void bfq_update_idle_window(struct bfq_data *bfqd,
- struct bfq_queue *bfqq,
- struct bfq_io_cq *bic)
+static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
+ struct bfq_queue *bfqq,
+ struct bfq_io_cq *bic)
{
- int enable_idle;
+ bool has_short_ttime = true;
- /* Don't idle for async or idle io prio class. */
- if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq))
+ /*
+ * No need to update has_short_ttime if bfqq is async or in
+ * idle io prio class, or if bfq_slice_idle is zero, because
+ * no device idling is performed for bfqq in this case.
+ */
+ if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) ||
+ bfqd->bfq_slice_idle == 0)
return;
/* Idle window just restored, statistics are meaningless. */
@@ -4004,27 +4016,22 @@ static void bfq_update_idle_window(struct bfq_data
*bfqd,
bfqd->bfq_wr_min_idle_time))
return;
- enable_idle = bfq_bfqq_idle_window(bfqq);
-
+ /* Think time is infinite if no process is linked to
+ * bfqq. Otherwise check average think time to
+ * decide whether to mark as has_short_ttime
+ */
if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
- bfqd->bfq_slice_idle == 0 ||
- (bfqd->hw_tag && BFQQ_SEEKY(bfqq) &&
- bfqq->wr_coeff == 1))
- enable_idle = 0;
- else if (bfq_sample_valid(bfqq->ttime.ttime_samples)) {
- if (bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle &&
- bfqq->wr_coeff == 1)
- enable_idle = 0;
- else
- enable_idle = 1;
- }
- bfq_log_bfqq(bfqd, bfqq, "update_idle_window: enable_idle %d",
- enable_idle);
+ (bfq_sample_valid(bfqq->ttime.ttime_samples) &&
+ bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle))
+ has_short_ttime = false;
+
+ bfq_log_bfqq(bfqd, bfqq, "update_has_short_ttime: has_short_ttime %d",
+ has_short_ttime);
- if (enable_idle)
- bfq_mark_bfqq_idle_window(bfqq);
+ if (has_short_ttime)
+ bfq_mark_bfqq_has_short_ttime(bfqq);
else
- bfq_clear_bfqq_idle_window(bfqq);
+ bfq_clear_bfqq_has_short_ttime(bfqq);
}
/*
@@ -4040,14 +4047,12 @@ static void bfq_rq_enqueued(struct bfq_data *bfqd,
struct bfq_queue *bfqq,
bfqq->meta_pending++;
bfq_update_io_thinktime(bfqd, bfqq);
+ bfq_update_has_short_ttime(bfqd, bfqq, bic);
bfq_update_io_seektime(bfqd, bfqq, rq);
- if (bfqq->entity.service > bfq_max_budget(bfqd) / 8 ||
- !BFQQ_SEEKY(bfqq))
- bfq_update_idle_window(bfqd, bfqq, bic);
bfq_log_bfqq(bfqd, bfqq,
- "rq_enqueued: idle_window=%d (seeky %d)",
- bfq_bfqq_idle_window(bfqq), BFQQ_SEEKY(bfqq));
+ "rq_enqueued: has_short_ttime=%d (seeky %d)",
+ bfq_bfqq_has_short_ttime(bfqq), BFQQ_SEEKY(bfqq));
bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 63e771a..53e2907 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -348,11 +348,11 @@ struct bfq_io_cq {
uint64_t blkcg_serial_nr; /* the current blkcg serial */
#endif
/*
- * Snapshot of the idle window before merging; taken to
- * remember this value while the queue is merged, so as to be
- * able to restore it in case of split.
+ * Snapshot of the has_short_time flag before merging; taken
+ * to remember its value while the queue is merged, so as to
+ * be able to restore it in case of split.
*/
- bool saved_idle_window;
+ bool saved_has_short_ttime;
/*
* Same purpose as the previous two fields for the I/O bound
* classification of a queue.
@@ -626,7 +626,7 @@ enum bfqq_state_flags {
* without idling the device
*/
BFQQF_fifo_expire, /* FIFO checked in this slice */
- BFQQF_idle_window, /* slice idling enabled */
+ BFQQF_has_short_ttime, /* queue has a short think time */
BFQQF_sync, /* synchronous queue */
BFQQF_IO_bound, /*
* bfqq has timed-out at least once
@@ -655,7 +655,7 @@ BFQ_BFQQ_FNS(busy);
BFQ_BFQQ_FNS(wait_request);
BFQ_BFQQ_FNS(non_blocking_wait_rq);
BFQ_BFQQ_FNS(fifo_expire);
-BFQ_BFQQ_FNS(idle_window);
+BFQ_BFQQ_FNS(has_short_ttime);
BFQ_BFQQ_FNS(sync);
BFQ_BFQQ_FNS(IO_bound);
BFQ_BFQQ_FNS(in_large_burst);
--
2.10.0
