On Thu, Aug 01, 2019 at 03:44:31PM -0700, ivo welch wrote:

hi richard---arthur and I are working with nbdkit v1.12.3 on qemu/kvm.

we found that our linux (ubuntu 16.04 32-bit) boot time from a local .img file went from about 10 seconds to about 3 minutes when using the nbdkit file plugin instead of directly connecting qemu to the file. on further inspection with bonnie++, we think the problem may be related to poor random seek performance:

In general I would expect some slowdown between using qemu directly against a file and using qemu -> nbd driver -> nbdkit -> file, but not nearly as much as you observed. This is running bonnie++ inside the guest? Are qemu & nbdkit running on the same machine? Are you using a TCP port or a Unix domain socket? (If TCP you may want to consider commits d088bf45, 0721aa9579 and 3842a080c). Which version of qemu is it? Rich.

DIRECT FROM QEMU TO .IMG FILE: ------------------------------------------------------------------------------------------------------------------------------ Version 1.97 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP TEST 4G 109468 11 58405 16 180613 33 3204 147 Latency 7125ms 5812ms 131ms 101ms ------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------

NBDKIT: ------------------------------------------------------------------------------------------------------------------------------ 1.97,1.97,TEST,1,1564697809,4G,,,,109468,11,58405,16,,,180613,33,3204,147,,,,,,,,,,,,,,,,,,,7125ms,5812ms,,131ms,101ms,,,,,, Version 1.97 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP TEST 4G 105761 11 58992 14 178472 30 39.3 6 Latency 8166ms 3683ms 187ms 1197ms ------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------

NBDKIT (-fv): ------------------------------------------------------------------------------------------------------------------------------ 1.97,1.97,TEST,1,1564698256,4G,,,,105761,11,58992,14,,,178472,30,39.3,6,,,,,,,,,,,,,,,,,,,8166ms,3683ms,,187ms,1197ms,,,,,, Version 1.97 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP TEST 4G 104941 10 56501 14 160557 28 39.9 6 Latency 15318ms 5200ms 101ms 1152ms

1.97,1.97,TEST,1,1564695086,4G,,,,104941,10,56501,14,,,160557,28,39.9,6,,,,,,,,,,,,,,,,,,,15318ms,5200ms,,101ms,1152ms,,,,,, ------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------

is this an error on our part? do you have any recommendations on what we could investigate next?

regards,

/iaw

-- Ivo Welch (ivo.welch@ucla.edu) http://www.ivo-welch.info/

-- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org