| Message ID | 20221209094442.36896-9-paolo.valente@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block, bfq: extend bfq to support multi-actuator drives | expand |
On 12/9/22 18:44, Paolo Valente wrote: > From: Davide Zini <davidezini2@gmail.com> > > Upon the invocation of its dispatch function, BFQ returns the next I/O > request of the in-service bfq_queue, unless some exception holds. One > such exception is that there is some underutilized actuator, different > from the actuator for which the in-service queue contains I/O, and > that some other bfq_queue happens to contain I/O for such an > actuator. In this case, the next I/O request of the latter bfq_queue, > and not of the in-service bfq_queue, is returned (I/O is injected from > that bfq_queue). To find such an actuator, a linear scan, in > increasing index order, is performed among actuators. > > Performing a linear scan entails a prioritization among actuators: an > underutilized actuator may be considered for injection only if all > actuators with a lower index are currently fully utilized, or if there > is no pending I/O for any lower-index actuator that happens to be > underutilized. > > This commits breaks this prioritization and tends to distribute > injection uniformly across actuators. This is obtained by adding the > following condition to the linear scan: even if an actuator A is > underutilized, A is however skipped if its load is higher than that of > the next actuator. > > Signed-off-by: Paolo Valente <paolo.valente@linaro.org> > Signed-off-by: Davide Zini <davidezini2@gmail.com> > --- > block/bfq-iosched.c | 18 +++++++++++++----- > 1 file changed, 13 insertions(+), 5 deletions(-) > > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c > index 527def05ce44..0ec8310331e1 100644 > --- a/block/bfq-iosched.c > +++ b/block/bfq-iosched.c > @@ -4830,10 +4830,16 @@ bfq_find_active_bfqq_for_actuator(struct bfq_data *bfqd, int idx) > > /* > * Perform a linear scan of each actuator, until an actuator is found > - * for which the following two conditions hold: the load of the > - * actuator is below the threshold (see comments on actuator_load_threshold > - * for details), and there is a queue that contains I/O for that > - * actuator. On success, return that queue. > + * for which the following three conditions hold: the load of the > + * actuator is below the threshold (see comments on > + * actuator_load_threshold for details) and lower than that of the > + * next actuator (comments on this extra condition below), and there > + * is a queue that contains I/O for that actuator. On success, return > + * that queue. > + * > + * Performing a plain linear scan entails a prioritization among > + * actuators. The extra condition above breaks this prioritization and > + * tends to distribute injection uniformly across actuators. > */ > static struct bfq_queue * > bfq_find_bfqq_for_underused_actuator(struct bfq_data *bfqd) > @@ -4841,7 +4847,9 @@ bfq_find_bfqq_for_underused_actuator(struct bfq_data *bfqd) > int i; > > for (i = 0 ; i < bfqd->num_actuators; i++) { > - if (bfqd->rq_in_driver[i] < bfqd->actuator_load_threshold) { > + if (bfqd->rq_in_driver[i] < bfqd->actuator_load_threshold && > + (i == bfqd->num_actuators - 1 || > + bfqd->rq_in_driver[i] < bfqd->rq_in_driver[i+1])) { > struct bfq_queue *bfqq = > bfq_find_active_bfqq_for_actuator(bfqd, i); > Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 527def05ce44..0ec8310331e1 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -4830,10 +4830,16 @@ bfq_find_active_bfqq_for_actuator(struct bfq_data *bfqd, int idx) /* * Perform a linear scan of each actuator, until an actuator is found - * for which the following two conditions hold: the load of the - * actuator is below the threshold (see comments on actuator_load_threshold - * for details), and there is a queue that contains I/O for that - * actuator. On success, return that queue. + * for which the following three conditions hold: the load of the + * actuator is below the threshold (see comments on + * actuator_load_threshold for details) and lower than that of the + * next actuator (comments on this extra condition below), and there + * is a queue that contains I/O for that actuator. On success, return + * that queue. + * + * Performing a plain linear scan entails a prioritization among + * actuators. The extra condition above breaks this prioritization and + * tends to distribute injection uniformly across actuators. */ static struct bfq_queue * bfq_find_bfqq_for_underused_actuator(struct bfq_data *bfqd) @@ -4841,7 +4847,9 @@ bfq_find_bfqq_for_underused_actuator(struct bfq_data *bfqd) int i; for (i = 0 ; i < bfqd->num_actuators; i++) { - if (bfqd->rq_in_driver[i] < bfqd->actuator_load_threshold) { + if (bfqd->rq_in_driver[i] < bfqd->actuator_load_threshold && + (i == bfqd->num_actuators - 1 || + bfqd->rq_in_driver[i] < bfqd->rq_in_driver[i+1])) { struct bfq_queue *bfqq = bfq_find_active_bfqq_for_actuator(bfqd, i);