On Wed, 15 Jun 2011 11:02:04 +0900 Namhyung Kim <namhyung@xxxxxxxxx> wrote:
> In the current scheme, multiple read request could be directed to
> the first active disk during recovery if there are several disk
> failure at the same time. Spreading those requests on other in-sync
> disks might be helpful.
I don't find this convincing either. Spreading requests over disks in a
haphazard way is not certain to improve anything and could easily cause
regressions.
For example if I have an 'n3' array on 3 devices, this will read alternately
from the first 2 devices while rebuilding the last. This is simply a waste.
One disk would be enough keep the rebuilding disk busy - the other should be
left of regular reads.
Again: if you can demonstrate a speed up in some configuration I'll be happy
to reconsider the patch.
Thanks,
NeilBrown
>
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxx>
> ---
> drivers/md/raid10.c | 10 +++++++---
> 1 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index dea73bdb99b8..d0188e49f881 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -1832,6 +1832,7 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr,
> if (!test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
> /* recovery... the complicated one */
> int j, k;
> + int last_read = -1;
> r10_bio = NULL;
>
> for (i=0 ; i<conf->raid_disks; i++) {
> @@ -1891,7 +1892,9 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr,
> &sync_blocks, still_degraded);
>
> for (j=0; j<conf->copies;j++) {
> - int d = r10_bio->devs[j].devnum;
> + int c = (last_read + j + 1) % conf->copies;
> + int d = r10_bio->devs[c].devnum;
> +
> if (!conf->mirrors[d].rdev ||
> !test_bit(In_sync, &conf->mirrors[d].rdev->flags))
> continue;
> @@ -1902,13 +1905,14 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr,
> bio->bi_private = r10_bio;
> bio->bi_end_io = end_sync_read;
> bio->bi_rw = READ;
> - bio->bi_sector = r10_bio->devs[j].addr +
> + bio->bi_sector = r10_bio->devs[c].addr +
> conf->mirrors[d].rdev->data_offset;
> bio->bi_bdev = conf->mirrors[d].rdev->bdev;
> atomic_inc(&conf->mirrors[d].rdev->nr_pending);
> atomic_inc(&r10_bio->remaining);
> - /* and we write to 'i' */
> + last_read = c;
>
> + /* and we write to 'i' */
> for (k=0; k<conf->copies; k++)
> if (r10_bio->devs[k].devnum == i)
> break;
--
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