[HyperV-2016] urandom performance issue...

Wei Hu weh at microsoft.com
Thu Aug 23 08:28:08 UTC 2018

I was not able to reproduce it on my test machine with Windows 10 (Build 17134) host and FreeBSD 11.2 release guest. I downloaded the 11.2 guest image directly from freebsd.org.

When running the dd command, I did see the guest OS hanged until the dd exited. However, there is no dmesg coming out during the run, neither did the host freeze.  I allocated 2GB memory and 1 vcpu to the guest.  The host performance monitor shows around 20% of system usage when the dd was running. It got back to single digit after it exited.


From: clement.moulin at gmail.com <clement.moulin at gmail.com> On Behalf Of Support SimpleRezo
Sent: Wednesday, August 22, 2018 9:04 PM
To: Wei Hu <weh at microsoft.com>
Cc: freebsd-virtualization at freebsd.org
Subject: Re: [HyperV-2016] urandom performance issue...

This is happening with Hyper-V Server 2016.
It's seems to not be the same on 2012 version, but the VM was on FreeBSD 10.3, not 11.2.


Le mer. 22 août 2018 à 11:38, Wei Hu <weh at microsoft.com<mailto:weh at microsoft.com>> a écrit :
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<mailto:owner-freebsd-virtualization at freebsd.org> <owner-freebsd-virtualization at freebsd.org<mailto: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<mailto:simplerezo at gmail.com>>
Cc: freebsd-virtualization at freebsd.org<mailto: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<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwiki.freebsd.org%2FHyperV&data=02%7C01%7Cweh%40microsoft.com%7C78a1c87c7675414d6fc408d6082fd29f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636705398826503446&sdata=UugmDCzy2VcrLF60MgxVpRUi5fgmB6SaG51%2B2ElC63A%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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