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
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