On Mon, Apr 27 2020 at 8:51pm -0400,
Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx> wrote:
> HST need to know the IO start time in order to predict path
> performance. For request-based multipath use the block layer
> io_start_time, while for BIO use the dm_io start_time.
>
> The dm_start_time_ns_from_clone function was suggested and implemented
> by Mike Snitzer <snitzer@xxxxxxxxxx>.
>
> Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> Cc: Khazhismel Kumykov <khazhy@xxxxxxxxxx>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
> ---
> drivers/md/dm-mpath.c | 25 +++++++++++++++----------
> drivers/md/dm-path-selector.h | 1 +
> drivers/md/dm.c | 10 ++++++++++
> include/linux/device-mapper.h | 2 ++
> 4 files changed, 28 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index 1ef4fc2e745b..7af3249948be 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -500,8 +500,9 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
> struct dm_mpath_io *mpio = get_mpio(map_context);
> struct request_queue *q;
> struct request *clone;
> - struct path_selector_io_data io_data = {
> + struct path_selector_io_data ps_io_data = {
> .nr_bytes = nr_bytes,
> + .io_start_time = rq->io_start_time_ns
> };
>
> /* Do we need to select a new pgpath? */
> @@ -552,7 +553,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
> if (pgpath->pg->ps.type->start_io)
> pgpath->pg->ps.type->start_io(&pgpath->pg->ps,
> &pgpath->path,
> - &io_data);
> + &ps_io_data);
> return DM_MAPIO_REMAPPED;
> }
>
> @@ -568,6 +569,7 @@ static void multipath_release_clone(struct request *clone,
> struct pgpath *pgpath = mpio->pgpath;
> struct path_selector_io_data ps_io_data = {
> .nr_bytes = mpio->nr_bytes,
> + .io_start_time = clone->io_start_time_ns,
> };
>
> if (pgpath && pgpath->pg->ps.type->end_io)
> @@ -623,8 +625,9 @@ static int __multipath_map_bio(struct multipath *m, struct bio *bio,
> struct dm_mpath_io *mpio)
> {
> struct pgpath *pgpath = __map_bio(m, bio);
> - struct path_selector_io_data io_data = {
> + struct path_selector_io_data ps_io_data = {
> .nr_bytes = mpio->nr_bytes,
> + .io_start_time = dm_start_time_ns_from_clone(bio)
> };
>
> if (IS_ERR(pgpath))
> @@ -646,7 +649,7 @@ static int __multipath_map_bio(struct multipath *m, struct bio *bio,
> if (pgpath->pg->ps.type->start_io)
> pgpath->pg->ps.type->start_io(&pgpath->pg->ps,
> &pgpath->path,
> - &io_data);
> + &ps_io_data);
> return DM_MAPIO_REMAPPED;
> }
>
io_start_time_ns isn't needed by any path selector's start_io method.
Please drop that from start_io and only pass it to the end_io hook.
(the need for dm_start_time_ns_from_clone() to access the more nested
nature of a bio clone's start_time showcases why we should avoid
needless collection of parameters that aren't required).
Thanks,
Mike
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