From: Michal Rostecki <mroste...@suse.com> This patch series adds a new raid1 read policy - roundrobin. For each request, it selects the mirror which has lower load than queue depth. Load is defined as the number of inflight requests + a penalty value (if the scheduled request is not local to the last processed request for a rotational disk).
The series consists of preparational changes which add necessary information to the btrfs_device struct and the change with the policy. This policy was tested with fio and compared with the default `pid` policy. The singlethreaded test has the following parameters: [global] name=btrfs-raid1-seqread filename=btrfs-raid1-seqread rw=read bs=64k direct=0 numjobs=1 time_based=0 [file1] size=10G ioengine=libaio and shows the following results: - raid1c3 with 3 HDDs: 3 x Segate Barracuda ST2000DM008 (2TB) * pid policy READ: bw=217MiB/s (228MB/s), 217MiB/s-217MiB/s (228MB/s-228MB/s), io=10.0GiB (10.7GB), run=47082-47082msec * roundrobin policy READ: bw=409MiB/s (429MB/s), 409MiB/s-409MiB/s (429MB/s-429MB/s), io=10.0GiB (10.7GB), run=25028-25028mse - raid1c3 with 2 HDDs and 1 SSD: 2 x Segate Barracuda ST2000DM008 (2TB) 1 x Crucial CT256M550SSD1 (256GB) * pid policy (the worst case when only HDDs were chosen) READ: bw=220MiB/s (231MB/s), 220MiB/s-220MiB/s (231MB/s-231MB/s), io=10.0GiB (10.7GB), run=46577-46577mse * pid policy (the best case when SSD was used as well) READ: bw=513MiB/s (538MB/s), 513MiB/s-513MiB/s (538MB/s-538MB/s), io=10.0GiB (10.7GB), run=19954-19954msec * roundrobin (there are no noticeable differences when testing multiple times) READ: bw=541MiB/s (567MB/s), 541MiB/s-541MiB/s (567MB/s-567MB/s), io=10.0GiB (10.7GB), run=18933-18933msec The multithreaded test has the following parameters: [global] name=btrfs-raid1-seqread filename=btrfs-raid1-seqread rw=read bs=64k direct=0 numjobs=8 time_based=0 [file1] size=10G ioengine=libaio and shows the following results: - raid1c3 with 3 HDDs: 3 x Segate Barracuda ST2000DM008 (2TB) 3 x Segate Barracuda ST2000DM008 (2TB) * pid policy READ: bw=1569MiB/s (1645MB/s), 196MiB/s-196MiB/s (206MB/s-206MB/s), io=80.0GiB (85.9GB), run=52210-52211msec * roundrobin READ: bw=1733MiB/s (1817MB/s), 217MiB/s-217MiB/s (227MB/s-227MB/s), io=80.0GiB (85.9GB), run=47269-47271msec - raid1c3 with 2 HDDs and 1 SSD: 2 x Segate Barracuda ST2000DM008 (2TB) 1 x Crucial CT256M550SSD1 (256GB) * pid policy READ: bw=1843MiB/s (1932MB/s), 230MiB/s-230MiB/s (242MB/s-242MB/s), io=80.0GiB (85.9GB), run=44449-44450msec * roundrobin READ: bw=2485MiB/s (2605MB/s), 311MiB/s-311MiB/s (326MB/s-326MB/s), io=80.0GiB (85.9GB), run=32969-32970msec To measure the performance of each policy and find optimal penalty values, I created scripts which are available here: https://gitlab.com/vadorovsky/btrfs-perf https://github.com/mrostecki/btrfs-perf Michal Rostecki (6): btrfs: Add inflight BIO request counter btrfs: Store the last device I/O offset btrfs: Add stripe_physical function btrfs: Check if the filesystem is has mixed type of devices btrfs: sysfs: Add directory for read policies btrfs: Add roundrobin raid1 read policy fs/btrfs/ctree.h | 3 + fs/btrfs/disk-io.c | 3 + fs/btrfs/sysfs.c | 144 ++++++++++++++++++++++++++---- fs/btrfs/volumes.c | 218 +++++++++++++++++++++++++++++++++++++++++++-- fs/btrfs/volumes.h | 22 +++++ 5 files changed, 366 insertions(+), 24 deletions(-) -- 2.30.0