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

From: liebrecht
Subject: Re: [Qemu-devel] Qemu the right way -[Subthread Cores]
Date: Wed, 26 Dec 2018 22:31:14 -0500
User-agent: Roundcube Webmail/1.3.3

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:

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

After this series, we bring down the average SPEC06int slowdown vs KVM
from 11.47x to 7.58x.

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