[HyperV-2016] urandom performance issue...

[John-Mark Gurney]

Support SimpleRezo wrote this message on Tue, Aug 21, 2018 at 19:06 +0200:
> I was figuring a performance issue of a FreeBSD on HyperV, after:
>   - moving it from an Hyper-V 2012 host to a Hyper-V 2016
>   - updating to FreeBSD 11.2 (custom kernel, but same issue with GENERIC)
> After loosing some times because i was thinking about hardware issue (disk
> controller was my first thought...) and testing with "dd
> if=/dev/urandom"... I discovered this...
> 
> I ran the following test... and quite surprised by the speed result!
> $ dd if=/dev/urandom of=/dev/null bs=10M count=3
> 3+0 records in
> 3+0 records out
> 31457280 bytes transferred in 27.960431 secs (1125064 bytes/sec)
> The test was also sometimes "freezing" the Hyper-V host!
> 
> Looking into "dmesg" i have found this:
> random: registering fast source Intel Secure Key RNG
> random: fast provider: "Intel Secure Key RNG"
> 
> So I rebuilt my KERNEL without "rdrand_rng" (didn't find another way to
> disable it...)... and performances went back to normal!
> 
> I think this issue should documented on https://wiki.freebsd.org/HyperV !

This is likely the same issue as:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=230808

If you're having troubles w/ the host freezing, this should probably
still be investigated as even w/ the excessive locking, it should never
freeze.

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."