On Thu, 28 Dec 2017 01:39:31 +0300
Timofey Titovets <nefelim4ag@xxxxxxxxx> wrote:
> Currently btrfs raid1/10 balancer blance requests to mirrors,
> based on pid % num of mirrors.
>
> Update logic and make it understood if underline device are non rotational.
>
> If one of mirrors are non rotational, then all read requests will be moved to
> non rotational device.
>
> If both of mirrors are non rotational, calculate sum of
> pending and in flight request for queue on that bdev and use
> device with least queue leght.
>
> P.S.
> Inspired by md-raid1 read balancing
>
> Signed-off-by: Timofey Titovets <nefelim4ag@xxxxxxxxx>
> ---
> fs/btrfs/volumes.c | 59
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 59
> insertions(+)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 9a04245003ab..98bc2433a920 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -5216,13 +5216,30 @@ int btrfs_is_parity_mirror(struct btrfs_fs_info
> *fs_info, u64 logical, u64 len) return ret;
> }
>
> +static inline int bdev_get_queue_len(struct block_device *bdev)
> +{
> + int sum = 0;
> + struct request_queue *rq = bdev_get_queue(bdev);
> +
> + sum += rq->nr_rqs[BLK_RW_SYNC] + rq->nr_rqs[BLK_RW_ASYNC];
> + sum += rq->in_flight[BLK_RW_SYNC] + rq->in_flight[BLK_RW_ASYNC];
> +
This won't work as expected if bdev is controlled by blk-mq, these
counters will be zero. AFAIK to get this info in block layer agnostic way
part_in_flight[1] has to be used. It extracts these counters approriately.
But it needs to be EXPORT_SYMBOL()'ed in block/genhd.c so we can continue
to build btrfs as module.
> + /*
> + * Try prevent switch for every sneeze
> + * By roundup output num by 2
> + */
> + return ALIGN(sum, 2);
> +}
> +
> static int find_live_mirror(struct btrfs_fs_info *fs_info,
> struct map_lookup *map, int first, int num,
> int optimal, int dev_replace_is_ongoing)
> {
> int i;
> int tolerance;
> + struct block_device *bdev;
> struct btrfs_device *srcdev;
> + bool all_bdev_nonrot = true;
>
> if (dev_replace_is_ongoing &&
> fs_info->dev_replace.cont_reading_from_srcdev_mode ==
> @@ -5231,6 +5248,48 @@ static int find_live_mirror(struct btrfs_fs_info
> *fs_info, else
> srcdev = NULL;
>
> + /*
> + * Optimal expected to be pid % num
> + * That's generaly ok for spinning rust drives
> + * But if one of mirror are non rotating,
> + * that bdev can show better performance
> + *
> + * if one of disks are non rotating:
> + * - set optimal to non rotating device
> + * if both disk are non rotating
> + * - set optimal to bdev with least queue
> + * If both disks are spinning rust:
> + * - leave old pid % nu,
> + */
> + for (i = 0; i < num; i++) {
> + bdev = map->stripes[i].dev->bdev;
> + if (!bdev)
> + continue;
> + if (blk_queue_nonrot(bdev_get_queue(bdev)))
> + optimal = i;
> + else
> + all_bdev_nonrot = false;
> + }
> +
> + if (all_bdev_nonrot) {
> + int qlen;
> + /* Forse following logic choise by init with some big number
> */
> + int optimal_dev_rq_count = 1 << 24;
Probably better to use INT_MAX macro instead.
[1] https://elixir.free-electrons.com/linux/v4.15-rc5/source/block/genhd.c#L68
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