Guest virtual CPUs limited to only 50% of host CPU

Guest virtual CPUs limited to only 50% of host CPU

[Drew Johnson]

Hi,

I am using Qemu-KVM-0.12.5 on Intel Xeon (Vt-x enabled) processors and
monitoring the system using htop on the host. On the processors that
are running Qemu-KVM I am seeing a 50/50 split between userspace and
guest ("gu:" in htop). I have pinned the vCPU qemu-kvm threads to
specific host CPUs using taskset. In the guest the CPUs are nearly
100% userspace in htop.

Does anyone have ideas on why this is? Is there a way I can get much
higher utilization for the guest virtual CPUs wrt the host?

Thanks in advance!

Re: Guest virtual CPUs limited to only 50% of host CPU

[Avi Kivity]

On 03/31/2011 11:03 PM, Drew Johnson wrote:
> Hi,
>
> I am using Qemu-KVM-0.12.5

This is somewhat old.  Try upgrading.

>   on Intel Xeon (Vt-x enabled) processors and
> monitoring the system using htop on the host. On the processors that
> are running Qemu-KVM I am seeing a 50/50 split between userspace and
> guest ("gu:" in htop). I have pinned the vCPU qemu-kvm threads to
> specific host CPUs using taskset. In the guest the CPUs are nearly
> 100% userspace in htop.
>
> Does anyone have ideas on why this is? Is there a way I can get much
> higher utilization for the guest virtual CPUs wrt the host?
>

Please build qemu with --disable-cpu-strip and run 'perf top' to see 
what's going on.

-- 
error compiling committee.c: too many arguments to function

Re: Guest virtual CPUs limited to only 50% of host CPU

[Drew Johnson]

Thanks for the reply. Turns out it was htop reporting it wrong. The
utime in /proc/stat already includes guest time.

On Tue, Apr 5, 2011 at 2:03 AM, Avi Kivity <avi@redhat.com> wrote:
> On 03/31/2011 11:03 PM, Drew Johnson wrote:
>>
>> Hi,
>>
>> I am using Qemu-KVM-0.12.5
>
> This is somewhat old.  Try upgrading.
>
>>  on Intel Xeon (Vt-x enabled) processors and
>> monitoring the system using htop on the host. On the processors that
>> are running Qemu-KVM I am seeing a 50/50 split between userspace and
>> guest ("gu:" in htop). I have pinned the vCPU qemu-kvm threads to
>> specific host CPUs using taskset. In the guest the CPUs are nearly
>> 100% userspace in htop.
>>
>> Does anyone have ideas on why this is? Is there a way I can get much
>> higher utilization for the guest virtual CPUs wrt the host?
>>
>
> Please build qemu with --disable-cpu-strip and run 'perf top' to see what's
> going on.
>
> --
> error compiling committee.c: too many arguments to function
>
>