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

Avi Kivity wrote:

quoted

quoted

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}.

For every vmexit, it does the entire thing, including vmload/vmsave

I haven't had a lot of luck eliminating vmload/vmsave.

, 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?

, segment reloading, and msr reloading.

Yeah, the VMX path is doing some clever things there.  A fair bit more 
could be deferred on SVM.

  It could use a lot of work.

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.

Regards,

Anthony Liguori



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