On 2019-02-10 16:35, Niclas Zeising wrote:
On 2019-02-08 10:27, Alexander Leidinger wrote:

I recently noticed some generic slowness myself. I experienced this during replacing disks in a raidz by bigger ones. Long story short, check top -s if you have vnlru running for a long period at high CPU... If yes increase kern.maxvnodes (I increased to 10 times). Note, we should improve the admin page in the FAQ, the vnlru entry could need a little bit more hints and explanations.

If you encounter the same issue we have probably introduced a change somewhere with an unintended side effect.


I'm seeing this as well, on 13-CURRENT.  I updated a computer from the last January snapshot (30 or 31 of January, I can't remember) and it seems disk IO is very slow.  I remember having a svn checkout taking a very long time, with the SVN process pegged at 100% according to top.  I can't see the vnlru process running though, but I haven't looked closely, and I haven't tried the maxvnodes workaround.  Something has changed though. This is systems using ZFS, both mirror and single disk.  Gstat shows disks are mostly idle.

I know this is a lousy bug report, but this, and the feeling that things are slower than usual, is what I have for now.

I did some more digging. In short, disabling options COVERAGE and options KCOV made my test case much faster.

My test:
boot system
create a new zfs dataset (zroot/home/test in my case)
time a checkout of https://svn.freebsd.org/base/head, putting the files in the new zfs dataset.

This is in no way scientific, since I only ran the test once on each kernel, and using something on the network means I'm susceptible to varying network speeds and so on, but. In this specific scenario, using a kernel without those options, it's about 3 times faster than with, at least on the computer where I ran the tests.

I noticed in the commit log that the coverage and kcov options has been disabled again, albeit for a different reason. Perhaps they should remain off, unless the extra runtime overhead can be disabled in runtime, similar to witness.
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