Re: [PATCH md-6.9 v2 02/10] md/raid1: record nonrot rdevs while adding/removing rdevs to conf

[Xiao Ni]

On Tue, Feb 27, 2024 at 8:09 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
>
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> For raid1, each read will iterate all the rdevs from conf and check if
> any rdev is non-rotational, then choose rdev with minimal IO inflight
> if so, or rdev with closest distance otherwise.
>
> Disk nonrot info can be changed through sysfs entry:
>
> /sys/block/[disk_name]/queue/rotational
>
> However, consider that this should only be used for testing, and user
> really shouldn't do this in real life. Record the number of non-rotational
> disks in conf, to avoid checking each rdev in IO fast path and simplify
> read_balance() a little bit.
>
> Co-developed-by: Paul Luse <paul.e.luse@xxxxxxxxxxxxxxx>
> Signed-off-by: Paul Luse <paul.e.luse@xxxxxxxxxxxxxxx>
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> ---
>  drivers/md/md.h    |  1 +
>  drivers/md/raid1.c | 17 ++++++++++-------
>  drivers/md/raid1.h |  1 +
>  3 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index a49ab04ab707..b2076a165c10 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -207,6 +207,7 @@ enum flag_bits {
>                                  * check if there is collision between raid1
>                                  * serial bios.
>                                  */
> +       Nonrot,                 /* non-rotational device (SSD) */
>  };
>
>  static inline int is_badblock(struct md_rdev *rdev, sector_t s, int sectors,
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index a145fe48b9ce..0fed01b06de9 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -599,7 +599,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>         int sectors;
>         int best_good_sectors;
>         int best_disk, best_dist_disk, best_pending_disk;
> -       int has_nonrot_disk;
>         int disk;
>         sector_t best_dist;
>         unsigned int min_pending;
> @@ -620,7 +619,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>         best_pending_disk = -1;
>         min_pending = UINT_MAX;
>         best_good_sectors = 0;
> -       has_nonrot_disk = 0;
>         choose_next_idle = 0;
>         clear_bit(R1BIO_FailFast, &r1_bio->state);
>
> @@ -637,7 +635,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>                 sector_t first_bad;
>                 int bad_sectors;
>                 unsigned int pending;
> -               bool nonrot;
>
>                 rdev = conf->mirrors[disk].rdev;
>                 if (r1_bio->bios[disk] == IO_BLOCKED
> @@ -703,8 +700,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>                         /* At least two disks to choose from so failfast is OK */
>                         set_bit(R1BIO_FailFast, &r1_bio->state);
>
> -               nonrot = bdev_nonrot(rdev->bdev);
> -               has_nonrot_disk |= nonrot;
>                 pending = atomic_read(&rdev->nr_pending);
>                 dist = abs(this_sector - conf->mirrors[disk].head_position);
>                 if (choose_first) {
> @@ -731,7 +726,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>                          * small, but not a big deal since when the second disk
>                          * starts IO, the first disk is likely still busy.
>                          */
> -                       if (nonrot && opt_iosize > 0 &&
> +                       if (test_bit(Nonrot, &rdev->flags) && opt_iosize > 0 &&
>                             mirror->seq_start != MaxSector &&
>                             mirror->next_seq_sect > opt_iosize &&
>                             mirror->next_seq_sect - opt_iosize >=
> @@ -763,7 +758,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
>          * mixed ratation/non-rotational disks depending on workload.
>          */
>         if (best_disk == -1) {
> -               if (has_nonrot_disk || min_pending == 0)
> +               if (READ_ONCE(conf->nonrot_disks) || min_pending == 0)
>                         best_disk = best_pending_disk;
>                 else
>                         best_disk = best_dist_disk;
> @@ -1819,6 +1814,11 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev)
>                 WRITE_ONCE(p[conf->raid_disks].rdev, rdev);
>         }
>
> +       if (!err && bdev_nonrot(rdev->bdev)) {
> +               set_bit(Nonrot, &rdev->flags);
> +               WRITE_ONCE(conf->nonrot_disks, conf->nonrot_disks + 1);
> +       }
> +

Hi Kuai

I noticed raid1_run->setup_conf is used to add rdev to conf when
creating raid1. raid1_add_disk is only used for --add/--re-add after
creating array. So we need to add the same logic in setup_conf?

Regards
Xiao
>         print_conf(conf);
>         return err;
>  }
> @@ -1883,6 +1883,9 @@ static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
>         }
>  abort:
>
> +       if (test_and_clear_bit(Nonrot, &rdev->flags))
> +               WRITE_ONCE(conf->nonrot_disks, conf->nonrot_disks - 1);
> +
>         print_conf(conf);
>         return err;
>  }
> diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
> index 14d4211a123a..5300cbaa58a4 100644
> --- a/drivers/md/raid1.h
> +++ b/drivers/md/raid1.h
> @@ -71,6 +71,7 @@ struct r1conf {
>                                                  * allow for replacements.
>                                                  */
>         int                     raid_disks;
> +       int                     nonrot_disks;
>
>         spinlock_t              device_lock;
>
> --
> 2.39.2
>