On Mon, Jun 04 2007, Carsten Otte wrote: > Jens Axboe wrote: > >Most people should not fiddle with it, the defaults are there for good > >reason. I can provide a blk_queue_unplug_thresholds(q, depth, delay) > >helper that you could use for the virtualized drivers, perhaps that > >would be better for that use? > Yea, we should'nt change the defaults without a good reason. That > would change things for all device drivers. > This interface provides all functionality we need. I think we need a > knob in /sys/block/mydevice/queue/ in addition to that.
Something like this, totally untested (but trivial, so it should work :-) diff --git a/block/elevator.c b/block/elevator.c index ce866eb..81e2a2d 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -638,7 +638,7 @@ void elv_insert(request_queue_t *q, struct request *rq, int where) int nrq = q->rq.count[READ] + q->rq.count[WRITE] - q->in_flight; - if (nrq >= q->unplug_thresh) + if (nrq >= q->unplug_thresh || !q->unplug_delay) __generic_unplug_device(q); } } diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c index 6b5173a..aaefb32 100644 --- a/block/ll_rw_blk.c +++ b/block/ll_rw_blk.c @@ -785,6 +785,30 @@ void blk_queue_dma_alignment(request_queue_t *q, int mask) EXPORT_SYMBOL(blk_queue_dma_alignment); /** + * blk_queue_unplug_threshold - set automatic unplug thresholds for the queue + * @q: the request queue for the device + * @depth: the queue depth at which to do unplug + * @delay: maximum unplug timer delay + * + * Description: + * Set the desired unplug depth/threshold and delay for a given queue. + * The block layer has a set of good defaults for this, so this function + * should ONLY be used by drivers for virtualized environments, where + * you could potentially have several layers of queues that each do their + * own delay. + * + * If in doubt, don't use this function! The settings can also be + * tweaked from sysfs. + * + **/ +void blk_queue_unplug_threshold(request_queue_t *q, unsigned int depth, + unsigned long delay) +{ + q->unplug_thresh = depth; + q->unplug_delay = delay; +} + +/** * blk_queue_find_tag - find a request by its tag and queue * @q: The request queue for the device * @tag: The tag of the request @@ -1550,7 +1574,8 @@ void blk_plug_device(request_queue_t *q) return; if (!test_and_set_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags)) { - mod_timer(&q->unplug_timer, jiffies + q->unplug_delay); + if (q->unplug_delay) + mod_timer(&q->unplug_timer, jiffies + q->unplug_delay); blk_add_trace_generic(q, NULL, 0, BLK_TA_PLUG); } } @@ -3975,6 +4000,54 @@ static ssize_t queue_max_hw_sectors_show(struct request_queue *q, char *page) return queue_var_show(max_hw_sectors_kb, (page)); } +static ssize_t queue_unplug_delay_show(struct request_queue *q, char *page) +{ + return queue_var_show(q->unplug_delay, page); +} + +/* + * We don't bother rearming a running timer. It's just not worth it, the + * next unplug will get it right. + */ +static ssize_t queue_unplug_delay_store(struct request_queue *q, + const char *page, size_t count) +{ + unsigned long delay; + int ret; + + ret = queue_var_store(&delay, page, count); + + spin_lock_irq(q->queue_lock); + q->unplug_delay = msecs_to_jiffies(delay); + spin_unlock_irq(q->queue_lock); + + return ret; +} + +static ssize_t queue_unplug_depth_show(struct request_queue *q, char *page) +{ + return queue_var_show(q->unplug_thresh, page); +} + +/* + * We don't bother unplugging if we depth was reduced and we just happened + * to have a current queue depth of somewhere in between the old and new + * value. + */ +static ssize_t queue_unplug_depth_store(struct request_queue *q, + const char *page, size_t count) +{ + unsigned long depth; + int ret; + + ret = queue_var_store(&depth, page, count); + + spin_lock_irq(q->queue_lock); + q->unplug_thresh = depth; + spin_unlock_irq(q->queue_lock); + + return ret; +} static struct queue_sysfs_entry queue_requests_entry = { .attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR }, @@ -4005,12 +4078,26 @@ static struct queue_sysfs_entry queue_iosched_entry = { .store = elv_iosched_store, }; +static struct queue_sysfs_entry queue_unplug_depth_entry = { + .attr = {.name = "unplug_depth", .mode = S_IRUGO | S_IWUSR }, + .show = queue_unplug_depth_show, + .store = queue_unplug_depth_store, +}; + +static struct queue_sysfs_entry queue_unplug_delay_entry = { + .attr = {.name = "unplug_delay_ms", .mode = S_IRUGO | S_IWUSR }, + .show = queue_unplug_delay_show, + .store = queue_unplug_delay_store, +}; + static struct attribute *default_attrs[] = { &queue_requests_entry.attr, &queue_ra_entry.attr, &queue_max_hw_sectors_entry.attr, &queue_max_sectors_entry.attr, &queue_iosched_entry.attr, + &queue_unplug_delay_entry.attr, + &queue_unplug_depth_entry.attr, NULL, }; diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index db5b00a..04c09d6 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -747,6 +747,7 @@ extern void blk_queue_prep_rq(request_queue_t *, prep_rq_fn *pfn); extern void blk_queue_merge_bvec(request_queue_t *, merge_bvec_fn *); extern void blk_queue_dma_alignment(request_queue_t *, int); extern void blk_queue_softirq_done(request_queue_t *, softirq_done_fn *); +extern void blk_queue_unplug_threshold(request_queue_t *q, unsigned int, unsigned long); extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev); extern int blk_queue_ordered(request_queue_t *, unsigned, prepare_flush_fn *); extern void blk_queue_issue_flush_fn(request_queue_t *, issue_flush_fn *); -- Jens Axboe ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. 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