[PATCH RFC 4/4] btrfs: introduce new read_policy round-robin
From: Anand Jain <hidden>
Date: 2021-01-11 09:42:46
Subsystem:
btrfs file system, filesystems (vfs and infrastructure), the rest · Maintainers:
Chris Mason, David Sterba, Alexander Viro, Christian Brauner, Linus Torvalds
Add round-robin read policy to route the read IO to the next device in the round-robin order. The chunk allocation and thus the stripe-index follows the order of free space available on devices. So to make the round-robin effective it shall follow the devid order instead of the stripe-index order. Signed-off-by: Anand Jain <redacted> -- RFC because: Provides terrible performance with the fio tests. I am not yet sure if there is any io workload or a block layer tuning that shall make this policy better. As of now just an experimental patch. fs/btrfs/sysfs.c | 2 +- fs/btrfs/volumes.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++ fs/btrfs/volumes.h | 3 +++ 3 files changed, 54 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 899b66c83db1..d40b0ff054ca 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c@@ -917,7 +917,7 @@ static bool strmatch(const char *buffer, const char *string) /* Must follow the order as in enum btrfs_read_policy */ static const char * const btrfs_read_policy_name[] = { "pid", "latency", - "device" }; + "device", "roundrobin" }; static ssize_t btrfs_read_policy_show(struct kobject *kobj, struct kobj_attribute *a, char *buf)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 50d4d54f7abd..60370b9121e0 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c@@ -5491,6 +5491,52 @@ int btrfs_is_parity_mirror(struct btrfs_fs_info *fs_info, u64 logical, u64 len) return ret; } +struct stripe_mirror { + u64 devid; + int map; +}; + +static int btrfs_cmp_devid(const void *a, const void *b) +{ + struct stripe_mirror *s1 = (struct stripe_mirror *)a; + struct stripe_mirror *s2 = (struct stripe_mirror *)b; + + if (s1->devid < s2->devid) + return -1; + if (s1->devid > s2->devid) + return 1; + return 0; +} + +static int btrfs_find_read_round_robin(struct map_lookup *map, int first, + int num_stripe) +{ + struct stripe_mirror stripes[4] = {0}; //4: for testing, works for now. + struct btrfs_fs_devices *fs_devices; + u64 devid; + int index, j, cnt; + int next_stripe; + + index = 0; + for (j = first; j < first + num_stripe; j++) { + devid = map->stripes[j].dev->devid; + + stripes[index].devid = devid; + stripes[index].map = j; + + index++; + } + + sort(stripes, num_stripe, sizeof(struct stripe_mirror), + btrfs_cmp_devid, NULL); + + fs_devices = map->stripes[first].dev->fs_devices; + cnt = atomic_inc_return(&fs_devices->total_reads); + next_stripe = stripes[cnt % num_stripe].map; + + return next_stripe; +} + static int btrfs_find_best_stripe(struct btrfs_fs_info *fs_info, struct map_lookup *map, int first, int num_stripe)
@@ -5579,6 +5625,10 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info, case BTRFS_READ_POLICY_DEVICE: preferred_mirror = btrfs_find_read_preferred(map, first, num_stripes); break; + case BTRFS_READ_POLICY_ROUND_ROBIN: + preferred_mirror = btrfs_find_read_round_robin(map, first, + num_stripes); + break; } if (dev_replace_is_ongoing &&
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 8d5a2cddc0ab..ce4490437f53 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h@@ -227,6 +227,8 @@ enum btrfs_read_policy { BTRFS_READ_POLICY_LATENCY, /* Use the device marked with READ_PREFERRED state */ BTRFS_READ_POLICY_DEVICE, + /* Distribute read IO equally across striped devices */ + BTRFS_READ_POLICY_ROUND_ROBIN, BTRFS_NR_READ_POLICY, };
@@ -286,6 +288,7 @@ struct btrfs_fs_devices { /* Policy used to read the mirrored stripes */ enum btrfs_read_policy read_policy; + atomic_t total_reads; }; #define BTRFS_BIO_INLINE_CSUM_SIZE 64
--
2.30.0