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Message-ID: <7b030433-518e-4fe7-976c-3ffb5f7f1a85@molgen.mpg.de>
Date: Thu, 29 Feb 2024 17:37:01 +0100
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: xni@...hat.com, paul.e.luse@...ux.intel.com, song@...nel.org,
neilb@...e.com, shli@...com, linux-raid@...r.kernel.org,
linux-kernel@...r.kernel.org, yukuai3@...wei.com, yi.zhang@...wei.com,
yangerkun@...wei.com
Subject: Re: [PATCH md-6.9 v4 03/11] md/raid1: record nonrot rdevs while
adding/removing rdevs to conf
Dear Yu,
Thank you for your patch.
Am 29.02.24 um 10:57 schrieb Yu Kuai:
> From: Yu Kuai <yukuai3@...wei.com>
>
> 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
The comma is not needed.
> read_balance() a little bit.
Just to make sure, I understood correctly. Changing
`/sys/block/[disk_name]/queue/rotational` will now not be considered
anymore, right?
For the summary, maybe you could also say “cache”. Maybe:
Cache attribute rotational while adding/removing rdevs to conf
> Co-developed-by: Paul Luse <paul.e.luse@...ux.intel.com>
> Signed-off-by: Paul Luse <paul.e.luse@...ux.intel.com>
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
> 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 6ec9998f6257..de6ea87d4d24 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;
> @@ -1768,6 +1763,11 @@ static bool raid1_add_conf(struct r1conf *conf, struct md_rdev *rdev, int disk,
> if (info->rdev)
> return false;
>
> + if (bdev_nonrot(rdev->bdev)) {
> + set_bit(Nonrot, &rdev->flags);
> + WRITE_ONCE(conf->nonrot_disks, conf->nonrot_disks + 1);
> + }
> +
> rdev->raid_disk = disk;
> info->head_position = 0;
> info->seq_start = MaxSector;
> @@ -1791,6 +1791,9 @@ static bool raid1_remove_conf(struct r1conf *conf, int disk)
> rdev->mddev->degraded < conf->raid_disks)
> return false;
>
> + if (test_and_clear_bit(Nonrot, &rdev->flags))
> + WRITE_ONCE(conf->nonrot_disks, conf->nonrot_disks - 1);
> +
> WRITE_ONCE(info->rdev, NULL);
> return true;
> }
> 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;
>
As you meant “fastpath” in the commit message, if I remember correctly,
this does not improve the performance in benchmarks, right?
Kind regards,
Paul
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