On 10/01/16 00:59, Bart Van Assche wrote:
> At least with dm-mq this patch reduces the number of multipath_busy()
> calls while scsi_dh_activate() is in progress from a few million to
> a few thousand.
>
> Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxx>
> Cc: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> ---
> drivers/md/dm-mpath.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index dd80af2..dd66653 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -343,12 +343,15 @@ static void multipath_init_per_bio_data(struct bio *bio, struct dm_mpath_io **mp
> * Path selection
> *-----------------------------------------------*/
>
> +/* Returns a value > 0 if path group initialization is still in progress. */
> static int __pg_init_all_paths(struct multipath *m)
> {
> struct pgpath *pgpath;
> unsigned long pg_init_delay = 0;
>
> - if (atomic_read(&m->pg_init_in_progress) || test_bit(MPATHF_PG_INIT_DISABLED, &m->flags))
> + if (atomic_read(&m->pg_init_in_progress))
> + return 1;
> + if (test_bit(MPATHF_PG_INIT_DISABLED, &m->flags))
> return 0;
>
> atomic_inc(&m->pg_init_count);
The patch changes the return value of __pg_init_all_paths() when
pg_init_in_progress is non-zero.
However, only caller of __pg_init_all_paths() that uses the return
value is pg_init_done() and it calls __pg_init_all_paths() only when
pg_init_in_progress is zero:
pg_init_done() {
...
spin_lock_irqsave(&m->lock, flags);
...
if (atomic_dec_return(&m->pg_init_in_progress) > 0)
goto out;
if (test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags)) {
if (delay_retry)
set_bit(MPATHF_PG_INIT_DELAY_RETRY, &m->flags);
else
clear_bit(MPATHF_PG_INIT_DELAY_RETRY, &m->flags);
if (__pg_init_all_paths(m))
goto out;
}
...
out:
spin_unlock_irqrestore(&m->lock, flags);
So I don't think the patch makes sense...
--
Jun'ichi Nomura, NEC Corporation / NEC Solution Innovators, Ltd.
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