Messages in this thread | | | Date | Fri, 08 May 2009 21:50:06 +0300 | From | Avi Kivity <> | Subject | Re: [RFC PATCH 0/3] generic hypercall support |
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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.
> > 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.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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