Re: [PATCH v2] DAX: enable iostat for read/write

Ross Zwisler
2016-10-17T17:30:08Z

On Mon, Oct 17, 2016 at 11:18:58AM -0600, Toshi Kani wrote:
> DAX IO path does not support iostat, but its metadata IO path does.
> Therefore, iostat shows metadata IO statistics only, which has been
> confusing to users.
>
> Add iostat support to the DAX read/write path.
>
> Note, iostat still does not support the DAX mmap path as it allows
> user applications to access directly.
>
> Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
> v2:
> - Set a minimum of one sector (Dan Williams)

What about Dave's feedback that this code just reimplements
generic_start_io_acct() and generic_end_io_acct()?

> ---
> fs/dax.c | 37 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 37 insertions(+)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 014defd..43e5e7a 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -144,6 +144,34 @@ static sector_t to_sector(const struct buffer_head *bh,
> return sector;
> }
>
> +static void dax_iostat_start(struct gendisk *disk, struct iov_iter *iter,
> + unsigned long *start)
> +{
> + int rw = iov_iter_rw(iter);
> + int sec = iov_iter_count(iter) >> 9;
> + int cpu = part_stat_lock();
> +
> + *start = jiffies;
> + part_round_stats(cpu, &disk->part0);
> + part_stat_inc(cpu, &disk->part0, ios[rw]);
> + part_stat_add(cpu, &disk->part0, sectors[rw], ((!sec) ? 1 : sec));
> + part_inc_in_flight(&disk->part0, rw);
> + part_stat_unlock();
> +}
> +
> +static void dax_iostat_end(struct gendisk *disk, struct iov_iter *iter,
> + unsigned long start)
> +{
> + unsigned long duration = jiffies - start;
> + int rw = iov_iter_rw(iter);
> + int cpu = part_stat_lock();
> +
> + part_stat_add(cpu, &disk->part0, ticks[rw], duration);
> + part_round_stats(cpu, &disk->part0);
> + part_dec_in_flight(&disk->part0, rw);
> + part_stat_unlock();
> +}
> +
> static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
> loff_t start, loff_t end, get_block_t get_block,
> struct buffer_head *bh)
> @@ -265,9 +293,12 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
> ssize_t retval = -EINVAL;
> loff_t pos = iocb->ki_pos;
> loff_t end = pos + iov_iter_count(iter);
> + struct gendisk *disk;
> + unsigned long start = 0;
>
> memset(&bh, 0, sizeof(bh));
> bh.b_bdev = inode->i_sb->s_bdev;
> + disk = bh.b_bdev->bd_disk;
>
> if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
> inode_lock(inode);
> @@ -276,8 +307,14 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
> if (!(flags & DIO_SKIP_DIO_COUNT))
> inode_dio_begin(inode);
>
> + if (blk_queue_io_stat(disk->queue))
> + dax_iostat_start(disk, iter, &start);
> +
> retval = dax_io(inode, iter, pos, end, get_block, &bh);
>
> + if (start)
> + dax_iostat_end(disk, iter, start);
> +
> if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
> inode_unlock(inode);
>