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 length 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 length then optimal,
repick to that mirror
For avoid round-robin request balancing,
lets round down queue length:
- By 8 for rotational devs
- By 2 for all non rotational devs
Some bench results from mail list
(Dmitrii Tcvetkov <demfl...@demfloro.ru>):
Benchmark summary (arithmetic mean of 3 runs):
Mainline Patch
------------------------------------
RAID1 | 18.9 MiB/s | 26.5 MiB/s
RAID10 | 30.7 MiB/s | 30.7 MiB/s
------------------------------------------------------------------------
mainline, fio got lucky to read from first HDD (quite slow HDD):
Jobs: 1 (f=1): [r(1)][100.0%][r=8456KiB/s,w=0KiB/s][r=264,w=0 IOPS]
read: IOPS=265, BW=8508KiB/s (8712kB/s)(499MiB/60070msec)
lat (msec): min=2, max=825, avg=60.17, stdev=65.06
------------------------------------------------------------------------
mainline, fio got lucky to read from second HDD (much more modern):
Jobs: 1 (f=1): [r(1)][8.7%][r=11.9MiB/s,w=0KiB/s][r=380,w=0 IOPS]
read: IOPS=378, BW=11.8MiB/s (12.4MB/s)(710MiB/60051msec)
lat (usec): min=416, max=644286, avg=42312.74, stdev=48518.56
------------------------------------------------------------------------
mainline, fio got lucky to read from an SSD:
Jobs: 1 (f=1): [r(1)][100.0%][r=436MiB/s,w=0KiB/s][r=13.9k,w=0 IOPS]
read: IOPS=13.9k, BW=433MiB/s (454MB/s)(25.4GiB/60002msec)
lat (usec): min=343, max=16319, avg=1152.52, stdev=245.36
------------------------------------------------------------------------
With the patch, 2 HDDs:
Jobs: 1 (f=1): [r(1)][100.0%][r=17.5MiB/s,w=0KiB/s][r=560,w=0 IOPS]
read: IOPS=560, BW=17.5MiB/s (18.4MB/s)(1053MiB/60052msec)
lat (usec): min=435, max=341037, avg=28511.64, stdev=30000.14
------------------------------------------------------------------------
With the patch, HDD(old one)+SSD:
Jobs: 1 (f=1): [r(1)][100.0%][r=371MiB/s,w=0KiB/s][r=11.9k,w=0 IOPS]
read: IOPS=11.6k, BW=361MiB/s (379MB/s)(21.2GiB/60084msec)
lat (usec): min=363, max=346752, avg=1381.73, stdev=6948.32
Changes:
v1 -> v2:
- Use helper part_in_flight() from genhd.c
to get queue length
- 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
v4 -> v5:
- Rebased on latest misc-next
v5 -> v6:
- Fix spelling
- Include bench results
Signed-off-by: Timofey Titovets <nefelim...@gmail.com>
Tested-by: Dmitrii Tcvetkov <demfl...@demfloro.ru>
Reviewed-by: Dmitrii Tcvetkov <demfl...@demfloro.ru>
---
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);
void part_in_flight_rw(struct request_queue *q, struct hd_struct *part,
unsigned int inflight[2])
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/raid/pq.h>
#include <linux/semaphore.h>
#include <linux/uuid.h>
+#include <linux/genhd.h>
#include <linux/list_sort.h>
#include "ctree.h"
#include "extent_map.h"
@@ -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 length 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 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;
+ 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 ==
--
2.17.0
