Messages in this thread | | | Subject | Re: [PATCH md-6.9 03/10] md/raid1: fix choose next idle in read_balance() | From | Yu Kuai <> | Date | Tue, 27 Feb 2024 10:38:01 +0800 |
| |
Hi,
在 2024/02/27 10:23, Xiao Ni 写道: > On Thu, Feb 22, 2024 at 4:04 PM Yu Kuai <yukuai1@huaweicloud.com> wrote: >> >> From: Yu Kuai <yukuai3@huawei.com> >> >> 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@linux.intel.com> >> Signed-off-by: Paul Luse <paul.e.luse@linux.intel.com> >> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >> --- >> 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 >> >> > > . >
| |