On 5/20/19 3:19 AM, Paolo Valente wrote: > > >> Il giorno 18 mag 2019, alle ore 22:50, Srivatsa S. Bhat <srivatsa@xxxxxxxxxxxxx> ha scritto: >> >> On 5/18/19 11:39 AM, Paolo Valente wrote: >>> I've addressed these issues in my last batch of improvements for BFQ, >>> which landed in the upcoming 5.2. If you give it a try, and still see >>> the problem, then I'll be glad to reproduce it, and hopefully fix it >>> for you. >>> >> >> Hi Paolo, >> >> Thank you for looking into this! >> >> I just tried current mainline at commit 72cf0b07, but unfortunately >> didn't see any improvement: >> >> dd if=/dev/zero of=/root/test.img bs=512 count=10000 oflag=dsync >> >> With mq-deadline, I get: >> >> 5120000 bytes (5.1 MB, 4.9 MiB) copied, 3.90981 s, 1.3 MB/s >> >> With bfq, I get: >> 5120000 bytes (5.1 MB, 4.9 MiB) copied, 84.8216 s, 60.4 kB/s >> > > Hi Srivatsa, > thanks for reproducing this on mainline. I seem to have reproduced a > bonsai-tree version of this issue. Before digging into the block > trace, I'd like to ask you for some feedback. > > First, in my test, the total throughput of the disk happens to be > about 20 times as high as that enjoyed by dd, regardless of the I/O > scheduler. I guess this massive overhead is normal with dsync, but > I'd like know whether it is about the same on your side. This will > help me understand whether I'll actually be analyzing about the same > problem as yours. > Do you mean to say the throughput obtained by dd'ing directly to the block device (bypassing the filesystem)? That does give me a 20x speedup with bs=512, but much more with a bigger block size (achieving a max throughput of about 110 MB/s). dd if=/dev/zero of=/dev/sdc bs=512 count=10000 conv=fsync 10000+0 records in 10000+0 records out 5120000 bytes (5.1 MB, 4.9 MiB) copied, 0.15257 s, 33.6 MB/s dd if=/dev/zero of=/dev/sdc bs=4k count=10000 conv=fsync 10000+0 records in 10000+0 records out 40960000 bytes (41 MB, 39 MiB) copied, 0.395081 s, 104 MB/s I'm testing this on a Toshiba MG03ACA1 (1TB) hard disk. > Second, the commands I used follow. Do they implement your test case > correctly? > > [root@localhost tmp]# mkdir /sys/fs/cgroup/blkio/testgrp > [root@localhost tmp]# echo $BASHPID > /sys/fs/cgroup/blkio/testgrp/cgroup.procs > [root@localhost tmp]# cat /sys/block/sda/queue/scheduler > [mq-deadline] bfq none > [root@localhost tmp]# dd if=/dev/zero of=/root/test.img bs=512 count=10000 oflag=dsync > 10000+0 record dentro > 10000+0 record fuori > 5120000 bytes (5,1 MB, 4,9 MiB) copied, 14,6892 s, 349 kB/s > [root@localhost tmp]# echo bfq > /sys/block/sda/queue/scheduler > [root@localhost tmp]# dd if=/dev/zero of=/root/test.img bs=512 count=10000 oflag=dsync > 10000+0 record dentro > 10000+0 record fuori > 5120000 bytes (5,1 MB, 4,9 MiB) copied, 20,1953 s, 254 kB/s > Yes, this is indeed the testcase, although I see a much bigger drop in performance with bfq, compared to the results from your setup. Regards, Srivatsa
