FreeBSD 10.1 disk performance lower than identical Linux Guest

FreeBSD 10.1 disk performance lower than identical Linux Guest

[Greg Langford]

Good Evening,

I am running CentOS 6.6 x86_64 as a KVM host and have a number of
guests running.

After some experimenting I have noticed something curious, FreeBSD
disk performance seems to be just over half of that of a Linux guest
with an identical configuration.

>From my understanding virtio is included in FreeBSD 10.0 onwards.

My CentOS guest has approx 130MB/s when using dd to read /dev/zero and
write it to a file on the guest file system. This is about the same
when doing the same on the hypervisor it's self. The stats are gained
using iotop on the hypervisor while the test is performed.

However the FreeBSD guest gets about 70MB/s maximum when performing
the same test and is running FreeBSD 10.1

Has anyone seen this before, is it a known issue or expected
behaviour? I have been scratching my head about it for a number of
days now.

Best Regards,
Greg Langford

Re: FreeBSD 10.1 disk performance lower than identical Linux Guest

[Ruben Kerkhof]

On Sat, Feb 21, 2015 at 7:59 PM, Greg Langford <greg@langford.me> wrote:
> Good Evening,

Hi Greg,
>
> I am running CentOS 6.6 x86_64 as a KVM host and have a number of
> guests running.
>
> After some experimenting I have noticed something curious, FreeBSD
> disk performance seems to be just over half of that of a Linux guest
> with an identical configuration.
>
> From my understanding virtio is included in FreeBSD 10.0 onwards.
>
> My CentOS guest has approx 130MB/s when using dd to read /dev/zero and
> write it to a file on the guest file system. This is about the same
> when doing the same on the hypervisor it's self. The stats are gained
> using iotop on the hypervisor while the test is performed.
>
> However the FreeBSD guest gets about 70MB/s maximum when performing
> the same test and is running FreeBSD 10.1
>
> Has anyone seen this before, is it a known issue or expected
> behaviour? I have been scratching my head about it for a number of
> days now.

There have been some performance improvements to the FreeBSD
virtio-blk driver in -CURRENT:
https://github.com/freebsd/freebsd/commit/6e8ba9083acb

Maybe these help?
>
> Best Regards,
> Greg Langford

Kind regards,
Ruben Kerkhof

Re: FreeBSD 10.1 disk performance lower than identical Linux Guest

[Stefan Hajnoczi]

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On Sat, Feb 21, 2015 at 06:59:23PM +0000, Greg Langford wrote:
> I am running CentOS 6.6 x86_64 as a KVM host and have a number of
> guests running.
> 
> After some experimenting I have noticed something curious, FreeBSD
> disk performance seems to be just over half of that of a Linux guest
> with an identical configuration.
> 
> From my understanding virtio is included in FreeBSD 10.0 onwards.
> 
> My CentOS guest has approx 130MB/s when using dd to read /dev/zero and
> write it to a file on the guest file system. This is about the same
> when doing the same on the hypervisor it's self. The stats are gained
> using iotop on the hypervisor while the test is performed.
> 
> However the FreeBSD guest gets about 70MB/s maximum when performing
> the same test and is running FreeBSD 10.1
> 
> Has anyone seen this before, is it a known issue or expected
> behaviour? I have been scratching my head about it for a number of
> days now.

Please post the dd command-line and the QEMU command-lines for launching
the Linux and FreeBSD guests.

Stefan

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