On 2018/04/25 17:15, Timofey Titovets wrote:
> 2018-04-25 10:54 GMT+03:00 Misono Tomohiro <misono.tomohiro@xxxxxxxxxxxxxx>:
>> On 2018/04/25 9:20, Timofey Titovets wrote:
>>> Currently btrfs raid1/10 balancer bаlance requests to mirrors,
>>> based on pid % num of mirrors.
>>>
>>> Make logic understood:
>>> - if one of underline devices are non rotational
>>> - Queue leght to underline devices
>>>
>>> By default try use pid % num_mirrors guessing, but:
>>> - If one of mirrors are non rotational, repick optimal to it
>>> - If underline mirror have less queue leght then optimal,
>>> repick to that mirror
>>>
>>> For avoid round-robin request balancing,
>>> lets round down queue leght:
>>> - By 8 for rotational devs
>>> - By 2 for all non rotational devs
>>>
>>> Changes:
>>> v1 -> v2:
>>> - Use helper part_in_flight() from genhd.c
>>> to get queue lenght
>>> - Move guess code to guess_optimal()
>>> - Change balancer logic, try use pid % mirror by default
>>> Make balancing on spinning rust if one of underline devices
>>> are overloaded
>>> v2 -> v3:
>>> - Fix arg for RAID10 - use sub_stripes, instead of num_stripes
>>> v3 -> v4:
>>> - Rebased on latest misc-next
>>>
>>> Signed-off-by: Timofey Titovets <nefelim4ag@xxxxxxxxx>
>>> ---
>>> block/genhd.c | 1 +
>>> fs/btrfs/volumes.c | 111 ++++++++++++++++++++++++++++++++++++++++++++-
>>> 2 files changed, 110 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/block/genhd.c b/block/genhd.c
>>> index 9656f9e9f99e..5ea5acc88d3c 100644
>>> --- a/block/genhd.c
>>> +++ b/block/genhd.c
>>> @@ -81,6 +81,7 @@ void part_in_flight(struct request_queue *q, struct hd_struct *part,
>>> atomic_read(&part->in_flight[1]);
>>> }
>>> }
>>> +EXPORT_SYMBOL_GPL(part_in_flight);
>>>
>>> struct hd_struct *__disk_get_part(struct gendisk *disk, int partno)
>>> {
>>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>>> index c95af358b71f..fa7dd6ac087f 100644
>>> --- a/fs/btrfs/volumes.c
>>> +++ b/fs/btrfs/volumes.c
>>> @@ -16,6 +16,7 @@
>>> #include <linux/semaphore.h>
>>> #include <linux/uuid.h>
>>> #include <linux/list_sort.h>
>>> +#include <linux/genhd.h>
>>> #include <asm/div64.h>
>>> #include "ctree.h"
>>> #include "extent_map.h"
>>> @@ -5148,7 +5149,7 @@ int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
>>> /*
>>> * There could be two corrupted data stripes, we need
>>> * to loop retry in order to rebuild the correct data.
>>> - *
>>> + *
>>> * Fail a stripe at a time on every retry except the
>>> * stripe under reconstruction.
>>> */
>>> @@ -5201,6 +5202,111 @@ int btrfs_is_parity_mirror(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
>>> return ret;
>>> }
>>>
>>> +/**
>>> + * bdev_get_queue_len - return rounded down in flight queue lenght of bdev
>>> + *
>>> + * @bdev: target bdev
>>> + * @round_down: round factor big for hdd and small for ssd, like 8 and 2
>>> + */
>>> +static int bdev_get_queue_len(struct block_device *bdev, int round_down)
>>> +{
>>> + int sum;
>>> + struct hd_struct *bd_part = bdev->bd_part;
>>> + struct request_queue *rq = bdev_get_queue(bdev);
>>> + uint32_t inflight[2] = {0, 0};
>>> +
>>> + part_in_flight(rq, bd_part, inflight);
>>> +
>>> + sum = max_t(uint32_t, inflight[0], inflight[1]);
>>> +
>>> + /*
>>> + * Try prevent switch for every sneeze
>>> + * By roundup output num by some value
>>> + */
>>> + return ALIGN_DOWN(sum, round_down);
>>> +}
>>> +
>>> +/**
>>> + * 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 leght 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 lenght
>>
>> The code looks always choosing the queue with the lowest length regardless
>> of the amount of queue length difference. So, this "significant" may be wrong?
>
> yes, but before code looks at queue len, we do round_down by 8,
> may be you confused because i hide ALIGN_DOWN in bdev_get_queue_len()
>
> I'm not think what this is "best" leveling queue leveling solution,
> but that's works.
> In theory ABS() <> some_num, can be used, but that's will lead to
> random send of some requests to hdd.
>
> i.e. for ABS() > 8:
> ssd hdd
> 9 0 -> hdd
> 9 1 -> ssd
> 10 1 -> hdd
> 10 2 -> ssd
> And so on.
>
> So in general that will looks like:
> ssd rount_down(7, 8) = 0, hdd round_down(0, 8) = 0
> ssd will be used
> And
> ssd round_down(9, 8) = 8, hdd round_down(0,8) = 0
> hdd will be used, while hdd qlen < 8.
>
> i.e. 'significant' depends on round_down factor.
>
> Thanks.
I see, thanks for the explanation.
Tomohiro Misono
>
>>> + * - Repick optimal if queue leght of other mirror are less
>>> + */
>>> +static int guess_optimal(struct map_lookup *map, int num, int optimal)
>>> +{
>>> + int i;
>>> + int round_down = 8;
>>> + int qlen[num];
>>> + bool is_nonrot[num];
>>> + bool all_bdev_nonrot = true;
>>> + bool all_bdev_rotate = true;
>>> + struct block_device *bdev;
>>> +
>>> + if (num == 1)
>>> + return optimal;
>>> +
>>> + /* Check accessible bdevs */
>>> + for (i = 0; i < num; i++) {
>>> + /* Init for missing bdevs */
>>> + is_nonrot[i] = false;
>>> + qlen[i] = INT_MAX;
>>> + 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 (num == 2 && qlen[0] != qlen[1]) {
>>> + if (qlen[0] < qlen[1])
>>> + return 0;
>>> + else
>>> + return 1;
>>> + }
>>> +
>>> + if (all_bdev_nonrot)
>>> + round_down = 2;
>>> +
>>> + for (i = 0; i < num; i++) {
>>> + if (qlen[i])
>>> + continue;
>>> + 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) {
>>> + for (i = 0; i < num; i++) {
>>> + if (is_nonrot[i])
>>> + optimal = i;
>>> + }
>>> + }
>>> +
>>> + for (i = 0; i < num; i++) {
>>> + if (qlen[optimal] > qlen[i])
>>> + 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)
>>> @@ -5219,7 +5325,8 @@ 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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