Cache queue_congestion_on/off_threshold

Chen, Kenneth W
2004-05-05T22:12:10Z

It's kind of redundant that queue_congestion_on/off_threshold gets
calculated on every I/O and they produce the same number over and
over again unless q->nr_requests gets changed (which is probably a
very rare event). Can we cache those values in the request_queue
structure?

- Ken

diff -Nurp linux-2.6.6-rc3/drivers/block/ll_rw_blk.c linux-2.6.6-rc3.blk/drivers/block/ll_rw_blk.c
--- linux-2.6.6-rc3/drivers/block/ll_rw_blk.c 2004-05-05 14:32:31.000000000 -0700
+++ linux-2.6.6-rc3.blk/drivers/block/ll_rw_blk.c 2004-05-05 15:04:59.000000000 -0700
@@ -70,14 +70,7 @@ EXPORT_SYMBOL(blk_max_pfn);
*/
static inline int queue_congestion_on_threshold(struct request_queue *q)
{
- int ret;
-
- ret = q->nr_requests - (q->nr_requests / 8) + 1;
-
- if (ret > q->nr_requests)
- ret = q->nr_requests;
-
- return ret;
+ return q->nr_congestion_on;
}

/*
@@ -85,14 +78,22 @@ static inline int queue_congestion_on_th
*/
static inline int queue_congestion_off_threshold(struct request_queue *q)
{
- int ret;
+ return q->nr_congestion_off;
+}

- ret = q->nr_requests - (q->nr_requests / 8) - 1;
+static inline void blk_queue_congestion_threshold(struct request_queue *q)
+{
+ int nr;

- if (ret < 1)
- ret = 1;
+ nr = q->nr_requests - (q->nr_requests / 8) + 1;
+ if (nr > q->nr_requests)
+ nr = q->nr_requests;
+ q->nr_congestion_on = nr;

- return ret;
+ nr = q->nr_requests - (q->nr_requests / 8) - 1;
+ if (nr < 1)
+ nr = 1;
+ q->nr_congestion_off = nr;
}

void clear_backing_dev_congested(struct backing_dev_info *bdi, int rw)
@@ -235,6 +236,7 @@ void blk_queue_make_request(request_queu
blk_queue_max_sectors(q, MAX_SECTORS);
blk_queue_hardsect_size(q, 512);
blk_queue_dma_alignment(q, 511);
+ blk_queue_congestion_threshold(q);

q->unplug_thresh = 4; /* hmm */
q->unplug_delay = (3 * HZ) / 1000; /* 3 milliseconds */
@@ -2953,6 +2955,7 @@ queue_requests_store(struct request_queu
int ret = queue_var_store(&q->nr_requests, page, count);
if (q->nr_requests < BLKDEV_MIN_RQ)
q->nr_requests = BLKDEV_MIN_RQ;
+ blk_queue_congestion_threshold(q);

if (rl->count[READ] >= queue_congestion_on_threshold(q))
set_queue_congested(q, READ);
diff -Nurp linux-2.6.6-rc3/include/linux/blkdev.h linux-2.6.6-rc3.blk/include/linux/blkdev.h
--- linux-2.6.6-rc3/include/linux/blkdev.h 2004-04-27 18:35:21.000000000 -0700
+++ linux-2.6.6-rc3.blk/include/linux/blkdev.h 2004-05-05 15:04:59.000000000 -0700
@@ -334,6 +334,8 @@ struct request_queue
* queue settings
*/
unsigned long nr_requests; /* Max # of requests */
+ unsigned int nr_congestion_on;
+ unsigned int nr_congestion_off;

unsigned short max_sectors;
unsigned short max_phys_segments;