On 18.05.2009, at 15:29, Avi Kivity wrote:
Alexander Graf wrote:
There's only a limited potential here (a factor of three, reducing
6 exits to 2, less the emulation overhead). There's a lot more to
be gained from nested npt, since you'll avoid most of the original
exits in the first place.
I think the reversed is the case. Look at those numbers (w2k8
bootup):
http://pastebin.ca/1423596
The only thing nested NPT would achieve is a reduction of #NPF
exits. But they are absolutely in the minority today already.
Normal #PF's do get directly passed to the guest already.
#NPF exits are caused when guest/host mappings change, which they
don't, or by mmio (which happens both for guest and nguest).
I don't understand how you can pass #PFs directly to the guest.
Surely the guest has enabled pagefault interception, and you need to
set up its vmcb?
Ugh - looks like I totally forgot to include #PF exits in my stats,
which is why I didn't see them.
Of course, this all depends on the workload. For kernbench style
benchmarks nested NPT probably gives you a bigger win, but anything
doing IO is slowed down way more than it has to now.
What is causing 17K pio exits/sec? What port numbers?
Any hints on how to easily find that out? For someone who's too stupid
to get kvmtrace working :-).
Alex
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
