From c9959059161ddd7bf4670cf47367033d6b2f79c4 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 25 Aug 2008 19:47:21 +0900 Subject: block: fix diskstats access There are two variants of stat functions - ones prefixed with double underbars which don't care about preemption and ones without which disable preemption before manipulating per-cpu counters. It's unclear whether the underbarred ones assume that preemtion is disabled on entry as some callers don't do that. This patch unifies diskstats access by implementing disk_stat_lock() and disk_stat_unlock() which take care of both RCU (for partition access) and preemption (for per-cpu counter access). diskstats access should always be enclosed between the two functions. As such, there's no need for the versions which disables preemption. They're removed and double underbars ones are renamed to drop the underbars. As an extra argument is added, there's no danger of using the old version unconverted. disk_stat_lock() uses get_cpu() and returns the cpu index and all diskstat functions which access per-cpu counters now has @cpu argument to help RT. This change adds RCU or preemption operations at some places but also collapses several preemption ops into one at others. Overall, the performance difference should be negligible as all involved ops are very lightweight per-cpu ones. Signed-off-by: Tejun Heo Cc: Peter Zijlstra Signed-off-by: Jens Axboe --- drivers/md/dm.c | 26 +++++++++++++++----------- 1 file changed, 15 insertions(+), 11 deletions(-) (limited to 'drivers/md/dm.c') diff --git a/drivers/md/dm.c b/drivers/md/dm.c index a78caad29996..653624792eaf 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -377,12 +377,13 @@ static void free_tio(struct mapped_device *md, struct dm_target_io *tio) static void start_io_acct(struct dm_io *io) { struct mapped_device *md = io->md; + int cpu; io->start_time = jiffies; - preempt_disable(); - disk_round_stats(dm_disk(md)); - preempt_enable(); + cpu = disk_stat_lock(); + disk_round_stats(cpu, dm_disk(md)); + disk_stat_unlock(); dm_disk(md)->in_flight = atomic_inc_return(&md->pending); } @@ -391,15 +392,15 @@ static int end_io_acct(struct dm_io *io) struct mapped_device *md = io->md; struct bio *bio = io->bio; unsigned long duration = jiffies - io->start_time; - int pending; + int pending, cpu; int rw = bio_data_dir(bio); - preempt_disable(); - disk_round_stats(dm_disk(md)); - preempt_enable(); - dm_disk(md)->in_flight = pending = atomic_dec_return(&md->pending); + cpu = disk_stat_lock(); + disk_round_stats(cpu, dm_disk(md)); + disk_stat_add(cpu, dm_disk(md), ticks[rw], duration); + disk_stat_unlock(); - disk_stat_add(dm_disk(md), ticks[rw], duration); + dm_disk(md)->in_flight = pending = atomic_dec_return(&md->pending); return !pending; } @@ -885,6 +886,7 @@ static int dm_request(struct request_queue *q, struct bio *bio) int r = -EIO; int rw = bio_data_dir(bio); struct mapped_device *md = q->queuedata; + int cpu; /* * There is no use in forwarding any barrier request since we can't @@ -897,8 +899,10 @@ static int dm_request(struct request_queue *q, struct bio *bio) down_read(&md->io_lock); - disk_stat_inc(dm_disk(md), ios[rw]); - disk_stat_add(dm_disk(md), sectors[rw], bio_sectors(bio)); + cpu = disk_stat_lock(); + disk_stat_inc(cpu, dm_disk(md), ios[rw]); + disk_stat_add(cpu, dm_disk(md), sectors[rw], bio_sectors(bio)); + disk_stat_unlock(); /* * If we're suspended we have to queue -- cgit v1.2.3