Re: [Qemu-devel] qemu processes

[Ryan Boyce]

Alex,

I have another KVM/qemu related CPU question. I am hoping you will be so
kind as to answer again. I have a Dell Poweredge T430 server running a
single Intel Xeon E5-2603 v3 CPU with 6 cores. I have 6 VMs running CentOS
7 via KVM. I am noticing some terrible host CPU performance when a VM runs
a simple process such as a recursive search on its file system. I see VM
CPU acting normally but the host CPU skyrockets to well over 100%. I have a
few ideas as to why this is but am hoping you might be able to point me in
the right direction. Thank you so much for your help!

Ryan

On Wed, Jun 12, 2019 at 12:50 PM Ryan Boyce <address@hidden> wrote:

> Thank you my friend!
>
> On Wed, Jun 12, 2019 at 12:48 PM Alex Bennée <address@hidden>
> wrote:
>
>> You've actually contacted the development list but I can answer the
>> question.
>>
>> QEMU is multi-threaded so there will be a thread per KVM based vCPU
>> (and also for TCG based vCPUs where MTTCG is enabled). There will also
>> be a number of additional threads created including at least one for
>> the main monitor thread and potentially additional threads for
>> servicing IO requests. So expect to see $SMP + 1 + n threads for each
>> QEMU instance.
>>
>> On Wed, 12 Jun 2019 at 16:32, Ryan Boyce <address@hidden> wrote:
>> >
>> > Hi Stefan,
>> >
>> > I am a big fan of your blog! In relation to your blog post,
>> >
>> http://blog.vmsplice.net/2011/03/qemu-internals-big-picture-overview.html
>> ,
>> > I have a question I am really hoping you can answer:
>> >
>> > When I start a VM, I see that the qemu-kvm processes start and run as
>> > "qemu-kvm..... -name "something1"...."
>> > My issue, though, is I see multiple processes running as "qemu-kvm.....
>> > -name "something1"...." and each of these processes has memory/cpu/disk
>> > mapped to it.
>> > Does qemu-kvm run VMs on a one-to-one VM-to-host process basis? Or does
>> > each virtual cpu on the guest get its own process on the host?
>> > For example, If I have a VM that has 4 virtual cpus, will I see 4
>> processes
>> > (PIDs) on the host or should I see just see one for the VM itself.
>> >
>> > Any help you can give would be GREATLY appreciated. Thank you!
>> >
>> > Ryan
>>
>>
>>
>> --
>> Alex Bennée
>> KVM/QEMU Hacker for Linaro
>>
>