Hi, 在 2024/02/27 10:23, Xiao Ni 写道:
On Thu, Feb 22, 2024 at 4:04 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:From: Yu Kuai <yukuai3@xxxxxxxxxx> Commit 12cee5a8a29e ("md/raid1: prevent merging too large request") add the case choose next idle in read_balance(): read_balance: for_each_rdev if(next_seq_sect == this_sector || disk == 0) -> sequential reads best_disk = disk; if (...) choose_next_idle = 1 continue; for_each_rdev -> iterate next rdev if (pending == 0) best_disk = disk; -> choose the next idle disk break; if (choose_next_idle) -> keep using this rdev if there are no other idle disk contine However, commit 2e52d449bcec ("md/raid1: add failfast handling for reads.") remove the code: - /* If device is idle, use it */ - if (pending == 0) { - best_disk = disk; - break; - } Hence choose next idle will never work now, fix this problem by following: 1) don't set best_disk in this case, read_balance() will choose the best disk after iterating all the disks; 2) add 'pending' so that other idle disk will be chosen; 3) set 'dist' to 0 so that if there is no other idle disk, and all disks are rotational, this disk will still be chosen; Fixes: 2e52d449bcec ("md/raid1: add failfast handling for reads.") 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/raid1.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index c60ea58ae8c5..d0bc67e6d068 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -604,7 +604,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect unsigned int min_pending; struct md_rdev *rdev; int choose_first; - int choose_next_idle; /* * Check if we can balance. We can balance on the whole @@ -619,7 +618,6 @@ 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; - choose_next_idle = 0; clear_bit(R1BIO_FailFast, &r1_bio->state); if ((conf->mddev->recovery_cp < this_sector + sectors) || @@ -712,7 +710,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect int opt_iosize = bdev_io_opt(rdev->bdev) >> 9; struct raid1_info *mirror = &conf->mirrors[disk]; - best_disk = disk; /* * If buffered sequential IO size exceeds optimal * iosize, check if there is idle disk. If yes, choose @@ -731,15 +728,21 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect mirror->next_seq_sect > opt_iosize && mirror->next_seq_sect - opt_iosize >= mirror->seq_start) { - choose_next_idle = 1; - continue; + /* + * Add 'pending' to avoid choosing this disk if + * there is other idle disk. + * Set 'dist' to 0, so that if there is no other + * idle disk and all disks are rotational, this + * disk will still be chosen. + */ + pending++; + dist = 0; + } else { + best_disk = disk; + break; } - break; }Hi Kuai I noticed something. In patch 12cee5a8a29e, it sets best_disk if it's a sequential read. If there are no other idle disks, it will read from the sequential disk. With this patch, it reads from the best_pending_disk even min_pending is not 0. It looks like a wrong behaviour?
Yes, nice catch, I didn't notice this yet... So there is a hidden logical, sequential IO priority is higher than minimal 'pending' selection, it's only less than 'choose_next_idle' where idle disk exist. Looks like if we want to keep this behaviour, we can add a 'sequential disk': if (is_sequential()) if (!should_choose_next()) return disk; ctl.sequential_disk = disk; ... if (ctl.min_pending != 0 && ctl.sequential_disk != -1) return ctl.sequential_disk; Thanks, Kuai
Best Regards Xiao- if (choose_next_idle) - continue; - if (min_pending > pending) { min_pending = pending; best_pending_disk = disk; -- 2.39.2.
