On Monday 10 December 2007 04:32, Jens Axboe wrote:
> I honestly don't know how to make this any clearer than I already did
> above.
Sure you do, you could cut out the rhetoric and save lots of bandwidth
thereby.
Yes, the q = bdev_get_queue(bio->bi_bdev) needs to be repeated inside
the submission loop, that was a flaw, thanks for the catch.
Regards,
Daniel
--- 2.6.24-rc3-mm.clean/block/ll_rw_blk.c 2007-12-04 14:45:25.000000000 -0800
+++ 2.6.24-rc3-mm/block/ll_rw_blk.c 2007-12-10 04:49:56.000000000 -0800
@@ -3210,9 +3210,9 @@ static inline int bio_check_eod(struct b
*/
static inline void __generic_make_request(struct bio *bio)
{
- struct request_queue *q;
+ struct request_queue *q = bdev_get_queue(bio->bi_bdev);
sector_t old_sector;
- int ret, nr_sectors = bio_sectors(bio);
+ int nr_sectors = bio_sectors(bio);
dev_t old_dev;
int err = -EIO;
@@ -3221,6 +3221,13 @@ static inline void __generic_make_reques
if (bio_check_eod(bio, nr_sectors))
goto end_io;
+ if (q && q->metric && !bio->bi_queue) {
+ int need = bio->bi_throttle = q->metric(bio);
+ bio->bi_queue = q;
+ /* FIXME: potential race if atomic_sub is called in the middle of condition check */
+ wait_event(q->throttle_wait, atomic_read(&q->available) >= need);
+ atomic_sub(need, &q->available);
+ }
/*
* Resolve the mapping until finished. (drivers are
* still free to implement/resolve their own stacking
@@ -3231,10 +3238,9 @@ static inline void __generic_make_reques
*/
old_sector = -1;
old_dev = 0;
- do {
+ while (1) {
char b[BDEVNAME_SIZE];
- q = bdev_get_queue(bio->bi_bdev);
if (!q) {
printk(KERN_ERR
"generic_make_request: Trying to access "
@@ -3282,8 +3288,10 @@ end_io:
goto end_io;
}
- ret = q->make_request_fn(q, bio);
- } while (ret);
+ if (!q->make_request_fn(q, bio))
+ return;
+ q = bdev_get_queue(bio->bi_bdev);
+ }
}
/*
--- 2.6.24-rc3-mm.clean/drivers/md/dm.c 2007-12-04 14:46:04.000000000 -0800
+++ 2.6.24-rc3-mm/drivers/md/dm.c 2007-12-04 23:31:41.000000000 -0800
@@ -889,6 +889,11 @@ static int dm_any_congested(void *conges
return r;
}
+static unsigned dm_metric(struct bio *bio)
+{
+ return bio->bi_vcnt;
+}
+
/*-----------------------------------------------------------------
* An IDR is used to keep track of allocated minor numbers.
*---------------------------------------------------------------*/
@@ -967,6 +972,7 @@ out:
static struct block_device_operations dm_blk_dops;
+#define DEFAULT_THROTTLE_CAPACITY 1000
/*
* Allocate and initialise a blank device with a given minor.
*/
@@ -1009,6 +1015,11 @@ static struct mapped_device *alloc_dev(i
goto bad1_free_minor;
md->queue->queuedata = md;
+ md->queue->metric = dm_metric;
+ /* A dm device constructor may change the throttle capacity */
+ atomic_set(&md->queue->available, md->queue->capacity = DEFAULT_THROTTLE_CAPACITY);
+ init_waitqueue_head(&md->queue->throttle_wait);
+
md->queue->backing_dev_info.congested_fn = dm_any_congested;
md->queue->backing_dev_info.congested_data = md;
blk_queue_make_request(md->queue, dm_request);
--- 2.6.24-rc3-mm.clean/fs/bio.c 2007-12-04 14:38:47.000000000 -0800
+++ 2.6.24-rc3-mm/fs/bio.c 2007-12-04 23:31:41.000000000 -0800
@@ -1007,6 +1007,13 @@ void bio_endio(struct bio *bio, int erro
else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
error = -EIO;
+ if (bio->bi_throttle) {
+ struct request_queue *q = bio->bi_queue;
+ bio->bi_throttle = 0; /* or detect multiple endio and err? */
+ atomic_add(bio->bi_throttle, &q->available);
+ wake_up(&q->throttle_wait);
+ }
+
if (bio->bi_end_io)
bio->bi_end_io(bio, error);
}
--- 2.6.24-rc3-mm.clean/include/linux/bio.h 2007-12-04 14:39:31.000000000 -0800
+++ 2.6.24-rc3-mm/include/linux/bio.h 2007-12-04 23:31:41.000000000 -0800
@@ -111,6 +111,9 @@ struct bio {
bio_end_io_t *bi_end_io;
atomic_t bi_cnt; /* pin count */
+ struct request_queue *bi_queue; /* for throttling */
+ unsigned bi_throttle; /* throttle metric */
+
void *bi_private;
bio_destructor_t *bi_destructor; /* destructor */
--- 2.6.24-rc3-mm.clean/include/linux/blkdev.h 2007-12-04 14:47:18.000000000 -0800
+++ 2.6.24-rc3-mm/include/linux/blkdev.h 2007-12-04 23:31:41.000000000 -0800
@@ -383,6 +383,10 @@ struct request_queue
struct work_struct unplug_work;
struct backing_dev_info backing_dev_info;
+ unsigned (*metric)(struct bio *bio); /* bio throttle metric */
+ wait_queue_head_t throttle_wait;
+ atomic_t available;
+ unsigned capacity;
/*
* The queue owner gets to use this for whatever they like.
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