diff options
Diffstat (limited to 'block/bfq-iosched.h')
| -rw-r--r-- | block/bfq-iosched.h | 22 |
1 files changed, 17 insertions, 5 deletions
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index fb28c255bcab..cc4ea8574483 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -71,17 +71,29 @@ struct bfq_service_tree { * * bfq_sched_data is the basic scheduler queue. It supports three * ioprio_classes, and can be used either as a toplevel queue or as an - * intermediate queue on a hierarchical setup. @next_in_service - * points to the active entity of the sched_data service trees that - * will be scheduled next. It is used to reduce the number of steps - * needed for each hierarchical-schedule update. + * intermediate queue in a hierarchical setup. * * The supported ioprio_classes are the same as in CFQ, in descending * priority order, IOPRIO_CLASS_RT, IOPRIO_CLASS_BE, IOPRIO_CLASS_IDLE. * Requests from higher priority queues are served before all the * requests from lower priority queues; among requests of the same * queue requests are served according to B-WF2Q+. - * All the fields are protected by the queue lock of the containing bfqd. + * + * The schedule is implemented by the service trees, plus the field + * @next_in_service, which points to the entity on the active trees + * that will be served next, if 1) no changes in the schedule occurs + * before the current in-service entity is expired, 2) the in-service + * queue becomes idle when it expires, and 3) if the entity pointed by + * in_service_entity is not a queue, then the in-service child entity + * of the entity pointed by in_service_entity becomes idle on + * expiration. This peculiar definition allows for the following + * optimization, not yet exploited: while a given entity is still in + * service, we already know which is the best candidate for next + * service among the other active entitities in the same parent + * entity. We can then quickly compare the timestamps of the + * in-service entity with those of such best candidate. + * + * All fields are protected by the lock of the containing bfqd. */ struct bfq_sched_data { /* entity in service */ |