2018-04-25 10:54 GMT+03:00 Misono Tomohiro <misono.tomoh...@jp.fujitsu.com>:
> 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 <nefelim...@gmail.com>
>> ---
>> 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.
>> + * - 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 ==
>>
>
--
Have a nice day,
Timofey.
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