Re: [Qemu-devel] KVM guest cpu L3 cache and cpufreq

[Benoît Canet]

Hello Eduardo,

I read a bit about caches on wikipedia.

If I understand correctly changing the CPUID L3 cache infos in QEMU will change
the value displayed in the guest /proc/cpuinfo but will not change the size of
the l3 cache used by the hardware. So I am chasing a cosmetic bug.
If it right ?

> > Do you have some recommandations regarding the other fields of the edx 
> > register ?
> 
> Probably it will be a good idea to let each CPU model have their own
> defaults for the cache information.

Do you mean querying the host CPUID registers and forwarding the values to the
guest ?

> 
> > What would be an acceptable user interface to set this ?
> 
> Things I can remember from the top of my head:
> 
>  * It would be interesting to redo this patch, before doing anything else:
>    
> https://github.com/ehabkost/qemu-hacks/commit/10b675fa1269a65a553586545fdbcd95ace79d65
>  * We need to keep compatibility on existing machine-types (not change
>    the cache size);
>  * If some information is reported on multiple CPUID leaves, we need to
>    keep them consistent with each other (see the FIXME comments on the
>    URL above);
I could write a patch to fix broken CPUID leaves.

But how would it work regarding compatibility ? Is it right to just fix the
leaves or does the machine type rule apply here ?

Best regards

Benoît