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
