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[BUGFIX/IMPROVEMENT,1/6] block, bfq: use half slice_idle as a threshold to check short ttime

Message ID 20210122181948.35660-2-paolo.valente@linaro.org (mailing list archive)
State New, archived
Headers show
Series block, bfq: first bath of fixes and improvements | expand

Commit Message

Paolo Valente Jan. 22, 2021, 6:19 p.m. UTC
The value of the I/O plugging (idling) timeout is used also as the
think-time threshold to decide whether a process has a short think
time.  In this respect, a good value of this timeout for rotational
drives is un the order of several ms. Yet, this is often too long a
time interval to be effective as a think-time threshold. This commit
mitigates this problem (by a lot, according to tests), by halving the

Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
 block/bfq-iosched.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
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diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 9e4eb0fc1c16..eb2ca32d5b63 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5238,12 +5238,13 @@  static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
 	/* 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
+	 * bfqq. Otherwise check average think time to decide whether
+	 * to mark as has_short_ttime. To this goal, compare average
+	 * think time with half the I/O-plugging timeout.
 	if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
 	    (bfq_sample_valid(bfqq->ttime.ttime_samples) &&
-	     bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle))
+	     bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle>>1))
 		has_short_ttime = false;
 	state_changed = has_short_ttime != bfq_bfqq_has_short_ttime(bfqq);