From: Jens Axboe <axboe@suse.de>
Here's a quickie that limits the queue depth to 1 by default, changable in
sysfs. There's room for improvement, if you want to play with things like
increasing the depth when anticipation doesn't work anyways.
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
drivers/block/as-iosched.c | 50 +++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 50 insertions(+)
diff -puN drivers/block/as-iosched.c~as-limit-queue-depth drivers/block/as-iosched.c
--- 25/drivers/block/as-iosched.c~as-limit-queue-depth 2005-05-03 20:53:53.000000000 -0700
+++ 25-akpm/drivers/block/as-iosched.c 2005-05-03 20:53:53.000000000 -0700
@@ -59,6 +59,11 @@
#define default_antic_expire ((HZ / 150) ? HZ / 150 : 1)
/*
+ * max in-flight at the hardware level
+ */
+#define default_queue_depth (1)
+
+/*
* Keep track of up to 20ms thinktimes. We can go as big as we like here,
* however huge values tend to interfere and not decay fast enough. A program
* might be in a non-io phase of operation. Waiting on user input for example,
@@ -126,6 +131,9 @@ struct as_data {
int ioc_finished; /* IO associated with io_context is finished */
int nr_dispatched;
+ unsigned long queue_depth;
+ int in_flight;
+
/*
* settings that change how the i/o scheduler behaves
*/
@@ -175,6 +183,7 @@ struct as_rq {
unsigned long expires;
unsigned int is_sync;
+ unsigned int in_flight;
enum arq_state state;
};
@@ -1018,6 +1027,13 @@ out_ioc:
put_io_context(arq->io_context);
out:
arq->state = AS_RQ_POSTSCHED;
+
+ if (arq->in_flight) {
+ WARN_ON(!ad->in_flight);
+
+ arq->in_flight = 0;
+ ad->in_flight--;
+ }
}
/*
@@ -1363,6 +1379,7 @@ static struct request *as_next_request(r
{
struct as_data *ad = q->elevator->elevator_data;
struct request *rq = NULL;
+ struct as_rq *arq;
/*
* if there are still requests on the dispatch queue, grab the first
@@ -1370,6 +1387,24 @@ static struct request *as_next_request(r
if (!list_empty(ad->dispatch) || as_dispatch_request(ad))
rq = list_entry_rq(ad->dispatch->next);
+ /*
+ * if no request was available, or if this isn't a normal fs request
+ * just pass that to the driver
+ */
+ if (!rq || ((arq = RQ_DATA(rq)) == NULL) || !blk_fs_request(rq))
+ return rq;
+
+ /*
+ * allow this request, if we are not exceeding the queue depth set
+ * by the user or if this request was already seen by the driver
+ */
+ if (arq->in_flight)
+ return rq;
+ else if (ad->in_flight >= ad->queue_depth)
+ return NULL;
+
+ arq->in_flight = 1;
+ ad->in_flight++;
return rq;
}
@@ -1469,6 +1504,12 @@ static void as_deactivate_request(reques
struct as_rq *arq = RQ_DATA(rq);
if (arq) {
+ if (arq->in_flight) {
+ WARN_ON(!ad->in_flight);
+
+ arq->in_flight = 0;
+ ad->in_flight--;
+ }
if (arq->state == AS_RQ_REMOVED) {
arq->state = AS_RQ_DISPATCHED;
if (arq->io_context && arq->io_context->aic)
@@ -1913,6 +1954,7 @@ static int as_init_queue(request_queue_t
ad->antic_expire = default_antic_expire;
ad->batch_expire[REQ_SYNC] = default_read_batch_expire;
ad->batch_expire[REQ_ASYNC] = default_write_batch_expire;
+ ad->queue_depth = default_queue_depth;
e->elevator_data = ad;
ad->current_batch_expires = jiffies + ad->batch_expire[REQ_SYNC];
@@ -1976,6 +2018,7 @@ SHOW_FUNCTION(as_writeexpire_show, ad->f
SHOW_FUNCTION(as_anticexpire_show, ad->antic_expire);
SHOW_FUNCTION(as_read_batchexpire_show, ad->batch_expire[REQ_SYNC]);
SHOW_FUNCTION(as_write_batchexpire_show, ad->batch_expire[REQ_ASYNC]);
+SHOW_FUNCTION(as_queue_depth_show, ad->queue_depth);
#undef SHOW_FUNCTION
#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
@@ -1996,6 +2039,7 @@ STORE_FUNCTION(as_read_batchexpire_store
&ad->batch_expire[REQ_SYNC], 0, INT_MAX);
STORE_FUNCTION(as_write_batchexpire_store,
&ad->batch_expire[REQ_ASYNC], 0, INT_MAX);
+STORE_FUNCTION(as_queue_depth_store, &ad->queue_depth, 1, INT_MAX);
#undef STORE_FUNCTION
static struct as_fs_entry as_est_entry = {
@@ -2027,6 +2071,11 @@ static struct as_fs_entry as_write_batch
.show = as_write_batchexpire_show,
.store = as_write_batchexpire_store,
};
+static struct as_fs_entry as_queue_depth_entry = {
+ .attr = {.name = "queue_depth", .mode = S_IRUGO | S_IWUSR },
+ .show = as_queue_depth_show,
+ .store = as_queue_depth_store,
+};
static struct attribute *default_attrs[] = {
&as_est_entry.attr,
@@ -2035,6 +2084,7 @@ static struct attribute *default_attrs[]
&as_anticexpire_entry.attr,
&as_read_batchexpire_entry.attr,
&as_write_batchexpire_entry.attr,
+ &as_queue_depth_entry.attr,
NULL,
};
_