> Il giorno 21 mag 2019, alle ore 00:45, Srivatsa S. Bhat <srivatsa@xxxxxxxxxxxxx> ha scritto: > > 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)? No no, I mean simply what follows. 1) in one terminal: [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 2) In a second terminal, while the dd is in progress in the first terminal: $ iostat -tmd /dev/sda 3 Linux 5.1.0+ (localhost.localdomain) 20/05/2019 _x86_64_ (2 CPU) ... 20/05/2019 11:40:17 Device tps MB_read/s MB_wrtn/s MB_read MB_wrtn sda 2288,00 0,00 9,77 0 29 20/05/2019 11:40:20 Device tps MB_read/s MB_wrtn/s MB_read MB_wrtn sda 2325,33 0,00 9,93 0 29 20/05/2019 11:40:23 Device tps MB_read/s MB_wrtn/s MB_read MB_wrtn sda 2351,33 0,00 10,05 0 30 ... As you can see, the overall throughput (~10 MB/s) is more than 20 times as high as the dd throughput (~350 KB/s). But the dd is the only source of I/O. Do you also see such a huge difference? Thanks, Paolo > 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
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