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Date: Wed, 16 Jul 2008 08:19:05 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Tejun Heo <tj@...nel.org>
Cc: jens.axboe@...cle.com, James.Bottomley@...senPartnership.com,
bharrosh@...asas.com, greg.freemyer@...il.com,
linux-scsi@...r.kernel.org, brking@...ux.vnet.ibm.com, liml@....ca,
viro@....linux.org.uk, linux-kernel@...r.kernel.org,
linux-ide@...r.kernel.org,
Paul E McKenney <paulmck@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 05/10] block: always use __{disk|part|all}_stat_*() and
kill non-underbarred versions
On Mon, 2008-07-14 at 16:12 +0900, Tejun Heo wrote:
> 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. In any case, stats are not
> critical data and errors don't lead to critical failures.
>
> However, consistently using the underbarred version and ensuring that
> they are called with preemption disabled doesn't incur noticeable
> overhead or even reduces overhead in some cases.
>
> * part stat manipulations need disk_map_sector_rcu() which involves
> read locking RCU anyway. Using rcu_read_lock_preempt() instead
> solves the problem nicely. On rcuclassic, this means no extra
> overhead.
>
> * Calls to the non-underbarred versions are converted to explicit
> preemtion disable and calls to respective underbarrded versions. As
> all such users had more than one consecutive stat ops, this reduces
> extra preemption disable/enables.
>
> * In drivers/md/dm.c::end_io_acct(), __disk_stat_add() call is moved
> into neighboring preemption disabled block.
>
> The conversion makes the stats usage more consistent and IMHO the
> added few preemption calls are well justified for that.
>
> As this change makes non-underbarred versions useless, non-underbarred
> stat functions and macros are killed. The next patch will drop
> underbars from the underbarred versions as it's superflous now. This
> is done as a separate step so that compile fails between this and the
> next patch if someone's left behind.
Aah, found what you use it for...
See, you need the preempt-off for something different than the RCU
usage, hence it doesn't make sense to mix that in. Use the regular
get_cpu/put_cpu stuff to fiddle with the percpu counters already.
So NAK on this one too.
> Signed-off-by: Tejun Heo <tj@...nel.org>
> ---
> block/blk-core.c | 16 +++++++-------
> block/blk-merge.c | 4 +-
> drivers/block/aoe/aoecmd.c | 12 +++++-----
> drivers/md/dm.c | 10 +++++---
> drivers/md/linear.c | 6 +++-
> drivers/md/multipath.c | 6 +++-
> drivers/md/raid0.c | 6 +++-
> drivers/md/raid1.c | 6 +++-
> drivers/md/raid10.c | 6 +++-
> drivers/md/raid5.c | 6 +++-
> include/linux/genhd.h | 48 --------------------------------------------
> 11 files changed, 46 insertions(+), 80 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 84292e1..3238ffe 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -60,7 +60,7 @@ static void drive_stat_acct(struct request *rq, int new_io)
> if (!blk_fs_request(rq) || !rq->rq_disk)
> return;
>
> - rcu_read_lock();
> + rcu_read_lock_preempt();
>
> part = disk_map_sector_rcu(rq->rq_disk, rq->sector);
> if (!new_io)
> @@ -74,7 +74,7 @@ static void drive_stat_acct(struct request *rq, int new_io)
> }
> }
>
> - rcu_read_unlock();
> + rcu_read_unlock_preempt();
> }
>
> void blk_queue_congestion_threshold(struct request_queue *q)
> @@ -1542,11 +1542,11 @@ static int __end_that_request_first(struct request *req, int error,
> const int rw = rq_data_dir(req);
> struct hd_struct *part;
>
> - rcu_read_lock();
> + rcu_read_lock_preempt();
> part = disk_map_sector_rcu(req->rq_disk, req->sector);
> - all_stat_add(req->rq_disk, part, sectors[rw],
> - nr_bytes >> 9, req->sector);
> - rcu_read_unlock();
> + __all_stat_add(req->rq_disk, part, sectors[rw],
> + nr_bytes >> 9, req->sector);
> + rcu_read_unlock_preempt();
> }
>
> total_bytes = bio_nbytes = 0;
> @@ -1732,7 +1732,7 @@ static void end_that_request_last(struct request *req, int error)
> const int rw = rq_data_dir(req);
> struct hd_struct *part;
>
> - rcu_read_lock();
> + rcu_read_lock_preempt();
>
> part = disk_map_sector_rcu(disk, req->sector);
>
> @@ -1745,7 +1745,7 @@ static void end_that_request_last(struct request *req, int error)
> part->in_flight--;
> }
>
> - rcu_read_unlock();
> + rcu_read_unlock_preempt();
> }
>
> if (req->end_io)
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 9be9b2f..55456c8 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -469,7 +469,7 @@ static int attempt_merge(struct request_queue *q, struct request *req,
> if (req->rq_disk) {
> struct hd_struct *part;
>
> - rcu_read_lock();
> + rcu_read_lock_preempt();
>
> part = disk_map_sector_rcu(req->rq_disk, req->sector);
> disk_round_stats(req->rq_disk);
> @@ -479,7 +479,7 @@ static int attempt_merge(struct request_queue *q, struct request *req,
> part->in_flight--;
> }
>
> - rcu_read_unlock();
> + rcu_read_unlock_preempt();
> }
>
> req->ioprio = ioprio_best(req->ioprio, next->ioprio);
> diff --git a/drivers/block/aoe/aoecmd.c b/drivers/block/aoe/aoecmd.c
> index 50ef9ea..7bd8c98 100644
> --- a/drivers/block/aoe/aoecmd.c
> +++ b/drivers/block/aoe/aoecmd.c
> @@ -757,15 +757,15 @@ diskstats(struct gendisk *disk, struct bio *bio, ulong duration, sector_t sector
> const int rw = bio_data_dir(bio);
> struct hd_struct *part;
>
> - rcu_read_lock();
> + rcu_read_lock_preempt();
>
> part = disk_map_sector_rcu(disk, sector);
> - all_stat_inc(disk, part, ios[rw], sector);
> - all_stat_add(disk, part, ticks[rw], duration, sector);
> - all_stat_add(disk, part, sectors[rw], n_sect, sector);
> - all_stat_add(disk, part, io_ticks, duration, sector);
> + __all_stat_inc(disk, part, ios[rw], sector);
> + __all_stat_add(disk, part, ticks[rw], duration, sector);
> + __all_stat_add(disk, part, sectors[rw], n_sect, sector);
> + __all_stat_add(disk, part, io_ticks, duration, sector);
>
> - rcu_read_unlock();
> + rcu_read_unlock_preempt();
> }
>
> void
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 923fea4..6918bb7 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -396,10 +396,10 @@ static int end_io_acct(struct dm_io *io)
>
> preempt_disable();
> disk_round_stats(dm_disk(md));
> + __disk_stat_add(dm_disk(md), ticks[rw], duration);
> preempt_enable();
> - dm_disk(md)->in_flight = pending = atomic_dec_return(&md->pending);
>
> - disk_stat_add(dm_disk(md), ticks[rw], duration);
> + dm_disk(md)->in_flight = pending = atomic_dec_return(&md->pending);
>
> return !pending;
> }
> @@ -850,8 +850,10 @@ 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));
> + preempt_disable();
> + __disk_stat_inc(dm_disk(md), ios[rw]);
> + __disk_stat_add(dm_disk(md), sectors[rw], bio_sectors(bio));
> + preempt_enable();
>
> /*
> * If we're suspended we have to queue
> diff --git a/drivers/md/linear.c b/drivers/md/linear.c
> index 1074824..ec35b8b 100644
> --- a/drivers/md/linear.c
> +++ b/drivers/md/linear.c
> @@ -322,8 +322,10 @@ static int linear_make_request (struct request_queue *q, struct bio *bio)
> return 0;
> }
>
> - disk_stat_inc(mddev->gendisk, ios[rw]);
> - disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
> + preempt_disable();
> + __disk_stat_inc(mddev->gendisk, ios[rw]);
> + __disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
> + preempt_enable();
>
> tmp_dev = which_dev(mddev, bio->bi_sector);
> block = bio->bi_sector >> 1;
> diff --git a/drivers/md/multipath.c b/drivers/md/multipath.c
> index e968116..aed8ea9 100644
> --- a/drivers/md/multipath.c
> +++ b/drivers/md/multipath.c
> @@ -158,8 +158,10 @@ static int multipath_make_request (struct request_queue *q, struct bio * bio)
> mp_bh->master_bio = bio;
> mp_bh->mddev = mddev;
>
> - disk_stat_inc(mddev->gendisk, ios[rw]);
> - disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
> + preempt_disable();
> + __disk_stat_inc(mddev->gendisk, ios[rw]);
> + __disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
> + preempt_enable();
>
> mp_bh->path = multipath_map(conf);
> if (mp_bh->path < 0) {
> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> index 914c04d..d0cdfe1 100644
> --- a/drivers/md/raid0.c
> +++ b/drivers/md/raid0.c
> @@ -403,8 +403,10 @@ static int raid0_make_request (struct request_queue *q, struct bio *bio)
> return 0;
> }
>
> - disk_stat_inc(mddev->gendisk, ios[rw]);
> - disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
> + preempt_disable();
> + __disk_stat_inc(mddev->gendisk, ios[rw]);
> + __disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
> + preempt_enable();
>
> chunk_size = mddev->chunk_size >> 10;
> chunk_sects = mddev->chunk_size >> 9;
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index c610b94..6687ffe 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -804,8 +804,10 @@ static int make_request(struct request_queue *q, struct bio * bio)
>
> bitmap = mddev->bitmap;
>
> - disk_stat_inc(mddev->gendisk, ios[rw]);
> - disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
> + preempt_disable();
> + __disk_stat_inc(mddev->gendisk, ios[rw]);
> + __disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
> + preempt_enable();
>
> /*
> * make_request() can abort the operation when READA is being
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index a71277b..1d644dc 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -838,8 +838,10 @@ static int make_request(struct request_queue *q, struct bio * bio)
> */
> wait_barrier(conf);
>
> - disk_stat_inc(mddev->gendisk, ios[rw]);
> - disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
> + preempt_disable();
> + __disk_stat_inc(mddev->gendisk, ios[rw]);
> + __disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
> + preempt_enable();
>
> r10_bio = mempool_alloc(conf->r10bio_pool, GFP_NOIO);
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 3b27df5..a869e58 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -3580,8 +3580,10 @@ static int make_request(struct request_queue *q, struct bio * bi)
>
> md_write_start(mddev, bi);
>
> - disk_stat_inc(mddev->gendisk, ios[rw]);
> - disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bi));
> + preempt_disable();
> + __disk_stat_inc(mddev->gendisk, ios[rw]);
> + __disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bi));
> + preempt_enable();
>
> if (rw == READ &&
> mddev->reshape_position == MaxSector &&
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 3e35945..87a338b 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -207,13 +207,6 @@ extern void disk_part_iter_stop(struct disk_part_iter *piter);
> extern struct hd_struct *disk_map_sector_rcu(struct gendisk *disk,
> sector_t sector);
>
> -/*
> - * Macros to operate on percpu disk statistics:
> - *
> - * The __ variants should only be called in critical sections. The full
> - * variants disable/enable preemption.
> - */
> -
> #ifdef CONFIG_SMP
> #define __disk_stat_add(gendiskp, field, addnd) \
> (per_cpu_ptr(gendiskp->dkstats, smp_processor_id())->field += addnd)
> @@ -292,63 +285,22 @@ static inline void part_stat_set_all(struct hd_struct *part, int value)
>
> #endif /* CONFIG_SMP */
>
> -#define disk_stat_add(gendiskp, field, addnd) \
> - do { \
> - preempt_disable(); \
> - __disk_stat_add(gendiskp, field, addnd); \
> - preempt_enable(); \
> - } while (0)
> -
> #define __disk_stat_dec(gendiskp, field) __disk_stat_add(gendiskp, field, -1)
> -#define disk_stat_dec(gendiskp, field) disk_stat_add(gendiskp, field, -1)
> -
> #define __disk_stat_inc(gendiskp, field) __disk_stat_add(gendiskp, field, 1)
> -#define disk_stat_inc(gendiskp, field) disk_stat_add(gendiskp, field, 1)
> -
> #define __disk_stat_sub(gendiskp, field, subnd) \
> __disk_stat_add(gendiskp, field, -subnd)
> -#define disk_stat_sub(gendiskp, field, subnd) \
> - disk_stat_add(gendiskp, field, -subnd)
> -
> -#define part_stat_add(gendiskp, field, addnd) \
> - do { \
> - preempt_disable(); \
> - __part_stat_add(gendiskp, field, addnd);\
> - preempt_enable(); \
> - } while (0)
>
> #define __part_stat_dec(gendiskp, field) __part_stat_add(gendiskp, field, -1)
> -#define part_stat_dec(gendiskp, field) part_stat_add(gendiskp, field, -1)
> -
> #define __part_stat_inc(gendiskp, field) __part_stat_add(gendiskp, field, 1)
> -#define part_stat_inc(gendiskp, field) part_stat_add(gendiskp, field, 1)
> -
> #define __part_stat_sub(gendiskp, field, subnd) \
> __part_stat_add(gendiskp, field, -subnd)
> -#define part_stat_sub(gendiskp, field, subnd) \
> - part_stat_add(gendiskp, field, -subnd)
> -
> -#define all_stat_add(gendiskp, part, field, addnd, sector) \
> - do { \
> - preempt_disable(); \
> - __all_stat_add(gendiskp, part, field, addnd, sector); \
> - preempt_enable(); \
> - } while (0)
>
> #define __all_stat_dec(gendiskp, field, sector) \
> __all_stat_add(gendiskp, field, -1, sector)
> -#define all_stat_dec(gendiskp, field, sector) \
> - all_stat_add(gendiskp, field, -1, sector)
> -
> #define __all_stat_inc(gendiskp, part, field, sector) \
> __all_stat_add(gendiskp, part, field, 1, sector)
> -#define all_stat_inc(gendiskp, part, field, sector) \
> - all_stat_add(gendiskp, part, field, 1, sector)
> -
> #define __all_stat_sub(gendiskp, part, field, subnd, sector) \
> __all_stat_add(gendiskp, part, field, -subnd, sector)
> -#define all_stat_sub(gendiskp, part, field, subnd, sector) \
> - all_stat_add(gendiskp, part, field, -subnd, sector)
>
> /* Inlines to alloc and free disk stats in struct gendisk */
> #ifdef CONFIG_SMP
--
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