Re: paravirtualization & cr3-cache feature

["richardvoigt-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org" <richardvoigt-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

> > Intel is indeed slower than AMD with this one.
> > I didn't measure such roundtrip specifically. We usually see that the
> > VMETNRY/VMEXIT cycle limits our performance (for io/mmio,..)
> > On Intel core duo we cannot get more than 150k-200k VMEXITS per second
> > for regular guest doing extensive IO.
> >

/me raises hand

Why so many vm switches?  First up, a typical I/O system maxes at
about 1Gb/s, right?  That would be a gigabit NIC, or striped RAID, or
something like that.  This suggests an average of only about 300
bytes/transfer, to get >150k individual transfers per second?  I
thought block I/O usually dealt with 1kbyte or more.  Next, we're
living in a world where most CPUs supporting the required extended
instruction set are multi-core, and you specifically said core duo.
Shouldn't an extensive I/O workload  tend toward one CPU in each VM,
with contraposed producer-consumer queues, and almost zero context
switches?

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