Re: [PATCH 4/5] KVM: Add hypercall queue for paravirt_ops implementation

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Anthony Liguori wrote:
> Avi Kivity wrote:
>>>> These numbers are pretty bad.  I'd like to improve them, even 
>>>> without PV.
>>>
>>> I agree.  Do you know what's missing at this point?  There isn't a 
>>> whole lot of state saving going on for the light weight exit paths 
>>> for SVM.
>>
>> The SVM code doesn't even have a lightweight vmexit path.  
>
> Sure it does.  Quite a lot is deferred to vcpu_{load,put}.

Ah, I forgot.  Yes, the syscall msrs are deferred.

>
>> For every vmexit, it does the entire thing, including vmload/vmsave
>
> I haven't had a lot of luck eliminating vmload/vmsave.
>

For x86_64, the only issue I see is with TR.  Unfortunately, I don't see 
a way around it.


>> , fpu switch (if needed)
>
> The FPU switch can really be avoided?  Is it safe to assume that the 
> KVM code isn't going to use any FPU operations?

Generally, kernel code does not use the fpu (when it does, it calls 
kernel_fpu_begin() and kernel_fpu_end()).  The vmx code avoids the switch.

Of course, if the guest doesn't use the fpu, the switch is avoided anyway.

>>
>> For kbuild vs. kernbench, I suspect that -j4 causes the shadow page 
>> table cache to thrash.  1024 pages may be enough for a single 
>> instance but not -j4.  Hopefully replacing the eviction algorithm 
>> (currently FIFO) will help.  Otherwise we'll need to resize the cache 
>> again.
>
> I naively tried to bump it to 2048 and hit a kmalloc limitation.
>

struct kvm is 22K on x86_64.  Adding 1024 pointers makes it 30K.  What 
error did you get?

We should probably make the hashtable a pointer, and allocate vcpus 
separately as well.

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


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