Re: [Qemu-devel] Qemu the right way -[Subthread Cores]

Re: [Qemu-devel] Qemu the right way -[Subthread Cores]

[Andrew Randrianasulu]

> Since I do not have networking sorted out yet I cannot update win7 pro, and it 
might be the updates which are needed for allowing more than two cpus.

hm, brief search on my side resulted in this tip:

https://answers.microsoft.com/en-us/windows/forum/windows_7-hardware/windows-7-professional-x64-only-showing-2-of-8/0155f525-df73-4642-a828-21b80d1564b0

----------
Some recommendations (in Windows, make sure you are running as Administrator):
 
- Run MSConfig -> Change to Boot tab -> Advanced Options -> "Number of 
Processors", make sure there is no check mark.
- Delete processor entries listed in Device Manager, then reboot.

-------------

(I don't think BIOS options from this answer really apply directly to qemu case)

also, if win (or some applications inside it) keep crashing with -cpu host, you 
can try to reload host (Linux) kvm module with additional option:

"options kvm ignore_msrs=1" line (without quotes) should be added to
 /etc/modprobe.d/kvm.conf

from 
https://www.passmark.com/forum/performancetest/4748-startup-error-number-4-on-qemu-bsod

Re: [Qemu-devel] Qemu the right way -[Subthread Cores]

[liebrecht]

For the record I have no crashes with
-cpu host It works perfectly. Although I can only see 2 cpus in windows 
with 4 showing up in devicemanager.

The first link you sent was actually the first thing I tried and I was 
already aware of that one.
It made no difference whatsoever.
My bios is latest on the rackserver , but it does not have the maximum 
core option in the bios.

Let me update the os to latest patches. I can vaguely remeber a similar 
problem running wi7 pro natively. I think out of the box you get win7 
home cpu limits and only after updates do you have pro lqarger cpu count 
activated. I may remeber wrong, but I will do that first and report 
back.


> Since I do not have networking sorted out yet I cannot update win7 pro, 
> and it
might be the updates which are needed for allowing more than two cpus.

hm, brief search on my side resulted in this tip:

https://answers.microsoft.com/en-us/windows/forum/windows_7-hardware/windows-7-professional-x64-only-showing-2-of-8/0155f525-df73-4642-a828-21b80d1564b0

----------
Some recommendations (in Windows, make sure you are running as 
Administrator):

- Run MSConfig -> Change to Boot tab -> Advanced Options -> "Number of
Processors", make sure there is no check mark.
- Delete processor entries listed in Device Manager, then reboot.

-------------

(I don't think BIOS options from this answer really apply directly to 
qemu case)

also, if win (or some applications inside it) keep crashing with -cpu 
host, you
can try to reload host (Linux) kvm module with additional option:

"options kvm ignore_msrs=1" line (without quotes) should be added to
  /etc/modprobe.d/kvm.conf

from
https://www.passmark.com/forum/performancetest/4748-startup-error-number-4-on-qemu-bsod

Re: [Qemu-devel] Qemu the right way -[Subthread Cores]

[liebrecht]

Thanks a million Andrew
-enable-kvm switch really solved the erratic on of switching off the 
mouse and sound.
All I get now are small pips and pops I will have to chase sown. Sounds 
like buffer overruns of some sort due to too small buffers on the linux 
receiving end. Dont know how to adjust that, but I am sure it is 
something like that. Sounds like a gramophone scratch every now and then 
which I know to be usually too small buffers.

But, you improved the situation enormously thanks.

Regarding software cpus.
I realized something like that must be going on.
I dont understand the justification to add cpus for the guest that 
doesnt exist. That can only end in trouble.

What I want is for the guest to use a real subcollection of amount of 
cores accessed by the guest. I have 24 available, but some of my 
software to be used with qemu needs at least 6 cores so I need to get 
past this strange 2cpu limit that is now showing up in win7 pro. Since I 
do not have networking sorted out yet I cannot update win7 pro, and it 
might be the updates which are needed for allowing more than two cpus.
I uses cpus and cores interactively as for the windows guest both are 
the same number and windows only name them cpus.

I just added a subthread to the subject line to distinguish between the 
three problems I have, Networking Sound and Cpu Count in the host.
"-cpu host" seems to be what I need, so I will back up the VM and try 
it.

Thanks you have been of really great help.


On 2018-12-26 21:48, Andrew Randrianasulu wrote:
> Hello!
> 
> just saw your question in qemu-devel and trying to answer
> 
> -------------------
> Now for a very important question.
> 
> If hardware virtualization was not switched on in bios will qemu refuse 
> to
> create more cpus? I just want to know if there are not bogus software 
> cpus or
> cores created by qemu and that it actually checks it can get real cores 
> from
> the machine and make it available to the host.
> ----------------
> 
> I think qemu will create as much 'software' cpus as you told it by 
> '-smp'
> directive IF you will not use hardware virtualization. And you can run 
> with
> more virtual cpus than physical number of cpus you actually have, just 
> ..it
> will be slower, not faster.
> 
> but without hw virtualization everything will be ..sloooow [1] .... so 
> I think
> you better to add -enable-kvm to your qemu command line.  Try to use 
> -cpu host
> if you are brave (win7 may not survive this..)
> 
> 
> [1] see for example
> https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg03710.html
> 
> After this series, we bring down the average SPEC06int slowdown vs KVM
> from 11.47x to 7.58x.