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[PATCH] optimise loop driver a bit 

Looks like locking can be optimised quite a lot.  Increase lock widths
slightly so lo_lock is taken fewer times per request.  Also it was quite
trivial to cover lo_pending with that lock, and remove the atomic
requirement.  This also makes memory ordering explicitly correct, which is
nice (not that I particularly saw any mem ordering bugs).

Test was reading 4 250MB files in parallel on ext2-on-tmpfs filesystem (1K
block size, 4K page size).  System is 2 socket Xeon with HT (4 thread).

intel:/home/npiggin# umount /dev/loop0 ; mount /dev/loop0 /mnt/loop ; /usr/bin/time ./mtloop.sh

Before:
0.24user 5.51system 0:02.84elapsed 202%CPU (0avgtext+0avgdata 0maxresident)k
0.19user 5.52system 0:02.88elapsed 198%CPU (0avgtext+0avgdata 0maxresident)k
0.19user 5.57system 0:02.89elapsed 198%CPU (0avgtext+0avgdata 0maxresident)k
0.22user 5.51system 0:02.90elapsed 197%CPU (0avgtext+0avgdata 0maxresident)k
0.19user 5.44system 0:02.91elapsed 193%CPU (0avgtext+0avgdata 0maxresident)k

After:
0.07user 2.34system 0:01.68elapsed 143%CPU (0avgtext+0avgdata 0maxresident)k
0.06user 2.37system 0:01.68elapsed 144%CPU (0avgtext+0avgdata 0maxresident)k
0.06user 2.39system 0:01.68elapsed 145%CPU (0avgtext+0avgdata 0maxresident)k
0.06user 2.36system 0:01.68elapsed 144%CPU (0avgtext+0avgdata 0maxresident)k
0.06user 2.42system 0:01.68elapsed 147%CPU (0avgtext+0avgdata 0maxresident)k

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Nick Piggin 2005-06-23 00:09:06 -07:00 committed by Linus Torvalds
parent ab4af03a40
commit 35a82d1a53
2 changed files with 39 additions and 44 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

81
drivers/block/loop.c
View File

@ -472,17 +472,11 @@ static int do_bio_filebacked(struct loop_device *lo, struct bio *bio)
*/
static void loop_add_bio(struct loop_device *lo, struct bio *bio)
{
unsigned long flags;
spin_lock_irqsave(&lo->lo_lock, flags);
if (lo->lo_biotail) {
lo->lo_biotail->bi_next = bio;
lo->lo_biotail = bio;
} else
lo->lo_bio = lo->lo_biotail = bio;
spin_unlock_irqrestore(&lo->lo_lock, flags);
up(&lo->lo_bh_mutex);
}
/*
@ -492,14 +486,12 @@ static struct bio *loop_get_bio(struct loop_device *lo)
{
struct bio *bio;
spin_lock_irq(&lo->lo_lock);
if ((bio = lo->lo_bio)) {
if (bio == lo->lo_biotail)
lo->lo_biotail = NULL;
lo->lo_bio = bio->bi_next;
bio->bi_next = NULL;
}
spin_unlock_irq(&lo->lo_lock);
return bio;
}
@ -509,35 +501,28 @@ static int loop_make_request(request_queue_t *q, struct bio *old_bio)
struct loop_device *lo = q->queuedata;
int rw = bio_rw(old_bio);
if (!lo)
goto out;
if (rw == READA)
rw = READ;
BUG_ON(!lo || (rw != READ && rw != WRITE));
spin_lock_irq(&lo->lo_lock);
if (lo->lo_state != Lo_bound)
goto inactive;
atomic_inc(&lo->lo_pending);
spin_unlock_irq(&lo->lo_lock);
if (rw == WRITE) {
if (lo->lo_flags & LO_FLAGS_READ_ONLY)
goto err;
} else if (rw == READA) {
rw = READ;
} else if (rw != READ) {
printk(KERN_ERR "loop: unknown command (%x)\n", rw);
goto err;
}
goto out;
if (unlikely(rw == WRITE && (lo->lo_flags & LO_FLAGS_READ_ONLY)))
goto out;
lo->lo_pending++;
loop_add_bio(lo, old_bio);
spin_unlock_irq(&lo->lo_lock);
up(&lo->lo_bh_mutex);
return 0;
err:
if (atomic_dec_and_test(&lo->lo_pending))
up(&lo->lo_bh_mutex);
out:
if (lo->lo_pending == 0)
up(&lo->lo_bh_mutex);
spin_unlock_irq(&lo->lo_lock);
bio_io_error(old_bio, old_bio->bi_size);
return 0;
inactive:
spin_unlock_irq(&lo->lo_lock);
goto out;
}
/*
@ -560,13 +545,11 @@ static void do_loop_switch(struct loop_device *, struct switch_request *);
static inline void loop_handle_bio(struct loop_device *lo, struct bio *bio)
{
int ret;
if (unlikely(!bio->bi_bdev)) {
do_loop_switch(lo, bio->bi_private);
bio_put(bio);
} else {
ret = do_bio_filebacked(lo, bio);
int ret = do_bio_filebacked(lo, bio);
bio_endio(bio, bio->bi_size, ret);
}
}
@ -594,7 +577,7 @@ static int loop_thread(void *data)
set_user_nice(current, -20);
lo->lo_state = Lo_bound;
atomic_inc(&lo->lo_pending);
lo->lo_pending = 1;
/*
* up sem, we are running
@ -602,26 +585,37 @@ static int loop_thread(void *data)
up(&lo->lo_sem);
for (;;) {
down_interruptible(&lo->lo_bh_mutex);
int pending;
/*
* could be upped because of tear-down, not because of
* pending work
* interruptible just to not contribute to load avg
*/
if (!atomic_read(&lo->lo_pending))
if (down_interruptible(&lo->lo_bh_mutex))
continue;
spin_lock_irq(&lo->lo_lock);
/*
* could be upped because of tear-down, not pending work
*/
if (unlikely(!lo->lo_pending)) {
spin_unlock_irq(&lo->lo_lock);
break;
}
bio = loop_get_bio(lo);
if (!bio) {
printk("loop: missing bio\n");
continue;
}
lo->lo_pending--;
pending = lo->lo_pending;
spin_unlock_irq(&lo->lo_lock);
BUG_ON(!bio);
loop_handle_bio(lo, bio);
/*
* upped both for pending work and tear-down, lo_pending
* will hit zero then
*/
if (atomic_dec_and_test(&lo->lo_pending))
if (unlikely(!pending))
break;
}
@ -900,7 +894,8 @@ static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev)
spin_lock_irq(&lo->lo_lock);
lo->lo_state = Lo_rundown;
if (atomic_dec_and_test(&lo->lo_pending))
lo->lo_pending--;
if (!lo->lo_pending)
up(&lo->lo_bh_mutex);
spin_unlock_irq(&lo->lo_lock);

2
include/linux/loop.h
View File

@ -61,7 +61,7 @@ struct loop_device {
struct semaphore lo_sem;
struct semaphore lo_ctl_mutex;
struct semaphore lo_bh_mutex;
atomic_t lo_pending;
int lo_pending;
request_queue_t *lo_queue;
};