Comment 2 for bug 1758621

Just tested again on new Ubuntu 18.04 with kernel 4.15. The direct synchronous small 4K write performance is still slower than kernel 4.4 on Ubuntu 16.04.

Are kernel 4.13 and 4.15 having write performance issue on qemu 2.11.x?

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# ubuntu bionic kernel 4.15. the direct synchronous write performance is still 93% slower than kernel 4.4 on ubuntu xenial.
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root@localhost:~# dd if=/dev/zero of=/tmp/test bs=4K count=256 oflag=direct,sync status=progress; rm /tmp/test
1048576 bytes (1.0 MB, 1.0 MiB) copied, 3.504 s, 299 kB/s
root@localhost:~# dd if=/dev/zero of=/tmp/test bs=4M count=256 oflag=direct,sync status=progress; rm /tmp/test
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 3.00597 s, 357 MB/s
root@localhost:~# uname -a
Linux localhost 4.15.0-20-generic #21-Ubuntu SMP Tue Apr 24 06:16:15 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux