Re: [RFC PATCH 0/3] generic hypercall support

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Avi Kivity wrote:
Anthony Liguori wrote:

And we're now getting close to the point where the difference is virtually meaningless.

At .14us, in order to see 1% CPU overhead added from PIO vs HC, you need 71429 exits.


If I read things correctly, you want the difference between PIO and PIOoHC, which is 210ns. But your point stands, 50,000 exits/sec will add 1% cpu overhead.

Right, the basic math still stands.


The non-x86 architecture argument isn't valid because other architectures either 1) don't use PCI at all (s390) and are already using hypercalls 2) use PCI, but do not have a dedicated hypercall instruction (PPC emb) or 3) have PIO (ia64).

ia64 uses mmio to emulate pio, so the cost may be different. I agree on x86 it's almost negligible.

Yes, I misunderstood that they actually emulated it like that. However, ia64 has no paravirtualization support today so surely, we aren't going to be justifying this via ia64, right?

Regards,

Anthony Liguori

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