[HyperV-2016] urandom performance issue...

Wei Hu weh at microsoft.com
Wed Aug 22 09:38:12 UTC 2018

Have you ever seen the same issue on Hyper-V 2012? What is the Windows version what you are running into the issue?


-----Original Message-----
From: owner-freebsd-virtualization at freebsd.org <owner-freebsd-virtualization at freebsd.org> On Behalf Of John-Mark Gurney
Sent: Wednesday, August 22, 2018 8:35 AM
To: Support SimpleRezo <simplerezo at gmail.com>
Cc: freebsd-virtualization at freebsd.org
Subject: Re: [HyperV-2016] urandom performance issue...

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://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwiki.freebsd.org%2FHyperV&data=02%7C01%7Cweh%40microsoft.com%7Cc42c865cb80e4ed2c95f08d607c74577%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636704949779065690&sdata=WaGPCp%2FggDUQMyrk49GAbe8TypqYGdpV2tgTg3sTqvk%3D&reserved=0 !

This is likely the same issue as:

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."
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