The backing device is a 7.2K SAS disk, in RAID0 (Megaraid sas controller).. Thanks for comment on data-offset. Will give that a try.. On Tue, Feb 28, 2017 at 6:55 PM, Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx> wrote: > On Wed, 22 Feb 2017, shiva rkreddy wrote: >> >> fio command without fsync: >> >> >> >> # fio -filename=/dev/bcache0 -direct=1 -ioengine=libaio -rw=randwrite >> >> -bs=4k -name=mytest -iodepth=1 -runtime=30 -time_based >> >> >> >> iops : 35k >> >> >> >> fio command with fsync: >> >> >> >> fio -filename=/dev/bcache0 -direct=1 -ioengine=libaio -rw=randwrite >> >> -bs=4k -name=mytest -iodepth=1 -runtime=30 -time_based -fsync=1 > > Try -runtime=25 since 30s is the default writeback delay. More below. > >> >> >> >> iops: 8.1k >> > >> >> I'm quite surprised by the drop in iops with fsync turned on. Is this >> >> expected or am I missing some basic setting? >> > >> > It's not uncommon that fsync would have a huge performance impact. >> > Without fsync, most of the data never hits the storage and is only >> > staying in the system memory. >> > >> > May I suggest that you try to measure the performance of the same tests >> > when the filesystem is created on the NVMe device directly, without >> > using bcache? You're likely to observe a similar pattern. >> >> I've tried fio directly on nvme device and without filesystem. The >> drop with fsync is not that significant; 44313 vs 42713 on a 30s >> randwrite run with iodepth=1 > > Try using `make-bcache --data-offset X ...` to align your backing device. > It defaults to an 8k offset which may not be optimal. By the way, what is > your backing device /dev/sdb? > > Try these, too: > > echo 0 > /sys/block/bcache0/bcache/sequential_cutoff > echo 10000000 > /sys/block/bcache0/bcache/cache/congested_read_threshold_us > echo 10000000 > /sys/block/bcache0/bcache/cache/congested_write_threshold_us > > > > > > -- > Eric Wheeler > > >> >> >> # fio -filename=/dev/nvme0n1 -direct=1 -ioengine=libaio -rw=randwrite >> -bs=4k -name=mytest -iodepth=1 -runtime=30 -time_based >> mytest: (g=0): rw=randwrite, bs=4K-4K/4K-4K/4K-4K, ioengine=libaio, iodepth=1 >> fio-2.1.3 >> Starting 1 process >> Jobs: 1 (f=1): [w] [100.0% done] [0KB/177.6MB/0KB /s] [0/45.5K/0 iops] >> [eta 00m:00s] >> mytest: (groupid=0, jobs=1): err= 0: pid=2131: Thu Feb 9 18:56:01 2017 >> write: io=5193.2MB, bw=177253KB/s, iops=44313, runt= 30001msec >> >> # fio -filename=/dev/nvme0n1 -direct=1 -ioengine=libaio -rw=randwrite >> -bs=4k -name=mytest -iodepth=1 -runtime=30 -time_based -fsync=1 >> mytest: (g=0): rw=randwrite, bs=4K-4K/4K-4K/4K-4K, ioengine=libaio, iodepth=1 >> fio-2.1.3 >> Starting 1 process >> Jobs: 1 (f=1): [w] [100.0% done] [0KB/167.4MB/0KB /s] [0/42.9K/0 iops] >> [eta 00m:00s] >> mytest: (groupid=0, jobs=1): err= 0: pid=2136: Thu Feb 9 19:04:54 2017 >> write: io=5005.5MB, bw=170853KB/s, iops=42713, runt= 30000msec >> >> >> On Wed, Feb 22, 2017 at 3:40 AM, Vojtech Pavlik <vojtech@xxxxxxxx> wrote: >> > On Tue, Feb 21, 2017 at 10:48:06AM -0600, shiva rkreddy wrote: >> > >> > >> > -- >> > Vojtech Pavlik >> > Director SUSE Labs >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-bcache" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
