On Sat, Jul 25, 2020 at 08:00:39PM +0800, Coly Li wrote:
> Commit 85750aeb748f ("bcache: use bio_{start,end}_io_acct") moves the
> io account code to the location after bio_set_dev(bio, dc->bdev) in
> cached_dev_make_request(). Then the account is performed incorrectly on
> backing device, indeed the I/O should be counted to bcache device like
> /dev/bcache0.
>
> With the mistaken I/O account, iostat does not display I/O counts for
> bcache device and all the numbers go to backing device. In writeback
> mode, the hard drive may have 340K+ IOPS which is impossible and wrong
> for spinning disk.
>
> This patch introduces bch_bio_start_io_acct() and bch_bio_end_io_acct(),
> which switches bio->bi_disk to bcache device before calling
> bio_start_io_acct() or bio_end_io_acct(). Now the I/Os are counted to
> bcache device, and bcache device, cache device and backing device have
> their correct I/O count information back.
Please switch to use disk_{start,end}_io_acct instead of hacking around
with bi_disk assignments.
