On 12/11/2018 12.58, Timofey Titovets wrote:
> From: Timofey Titovets <nefelim...@gmail.com>
>
> Currently btrfs raid1/10 balancer bаlance requests to mirrors,
> based on pid % num of mirrors.
[...]
> v6 -> v7:
> - Fixes based on Nikolay Borisov review:
> * Assume num == 2
> * Remove "for" loop based on that assumption, where possible
> * No functional changes
>
> Signed-off-by: Timofey Titovets <nefelim...@gmail.com>
> Tested-by: Dmitrii Tcvetkov <demfl...@demfloro.ru>
> Reviewed-by: Dmitrii Tcvetkov <demfl...@demfloro.ru>
> ---
[...]
> +/**
> + * guess_optimal - return guessed optimal mirror
> + *
> + * Optimal expected to be pid % num_stripes
> + *
> + * That's generaly ok for spread load
> + * Add some balancer based on queue length to device
> + *
> + * Basic ideas:
> + * - Sequential read generate low amount of request
> + * so if load of drives are equal, use pid % num_stripes balancing
> + * - For mixed rotate/non-rotate mirrors, pick non-rotate as optimal
> + * and repick if other dev have "significant" less queue length
> + * - Repick optimal if queue length of other mirror are less
> + */
> +static int guess_optimal(struct map_lookup *map, int num, int optimal)
> +{
> + int i;
> + int round_down = 8;
> + /* Init for missing bdevs */
> + int qlen[2] = { INT_MAX, INT_MAX };
> + bool is_nonrot[2] = { false, false };
> + bool all_bdev_nonrot = true;
> + bool all_bdev_rotate = true;
> + struct block_device *bdev;
> +
> + ASSERT(num == 2);
> +
> + /* Check accessible bdevs */> + for (i = 0; i < 2; i++) {
>From your function comment, it is not clear why you are comparing "num" to
>"2". Pay attention that there are somewhere some patches which implement raid
>profile with higher redundancy (IIRC up to 4). I suggest to put your
>assumption also in the comment ("...this function works up to 2 mirrors...")
>and, better, add a define like
#define BTRFS_MAX_RAID1_RAID10_MIRRORS 2
And replace "2" with BTRFS_MAX_RAID1_RAID10_MIRRORS
> + bdev = map->stripes[i].dev->bdev;
> + if (bdev) {
> + qlen[i] = 0;
> + is_nonrot[i] = blk_queue_nonrot(bdev_get_queue(bdev));
> + if (is_nonrot[i])
> + all_bdev_rotate = false;
> + else
> + all_bdev_nonrot = false;
> + }
> + }
> +
> + /*
> + * Don't bother with computation
> + * if only one of two bdevs are accessible
> + */
> + if (qlen[0] == INT_MAX)
> + return 1;
> + if (qlen[1] == INT_MAX)
> + return 0;
> +
> + if (all_bdev_nonrot)
> + round_down = 2;
> +
> + for (i = 0; i < 2; i++) {
> + bdev = map->stripes[i].dev->bdev;
> + qlen[i] = bdev_get_queue_len(bdev, round_down);
> + }
> +
> + /* For mixed case, pick non rotational dev as optimal */
> + if (all_bdev_rotate == all_bdev_nonrot) {
> + if (is_nonrot[0])
> + optimal = 0;
> + else
> + optimal = 1;
> + }
> +
> + if (qlen[optimal] > qlen[(optimal + 1) % 2])
> + optimal = i;
> +
> + return optimal;
> +}
> +
> static int find_live_mirror(struct btrfs_fs_info *fs_info,
> struct map_lookup *map, int first,
> int dev_replace_is_ongoing)
> @@ -5177,7 +5274,8 @@ static int find_live_mirror(struct btrfs_fs_info
> *fs_info,
> else
> num_stripes = map->num_stripes;
>
> - preferred_mirror = first + current->pid % num_stripes;
> + preferred_mirror = first + guess_optimal(map, num_stripes,
> + current->pid % num_stripes);
>
> if (dev_replace_is_ongoing &&
> fs_info->dev_replace.cont_reading_from_srcdev_mode ==
>
--
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