windows PIO question

[Nikola Ciprich <nikola.ciprich@linuxbox.cz>]

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Hello everybody,

I'm a bit confused regarding windows guests and PIO.. some time ago, I was trying
to find out, why one of my windows guests was running terribly slow.
After checking the trace-cmd output, Avi stated that windows were using PIO instead
of DMA, after changing that, windows indeed got a lot faster. I didn't check  traces
 after that, but I'm now testing host with two windows 2003 guests, and checking the
trac-cmd output, I see a lot of kvm_pio calls.
While windows don't seem to be running particularly slow, they're not especially
fast either, and I'm wandering whether this could be related. But checking IDE
bus in guests, they seem to be using DMA which confuses me...
so my questions is, what are the kvm_pio operations I see in traces, and how can
I tell what is OK and what is wrong, regarding disks DMA/PIO?
If somebody could shed some light on this for me, I'd be very grateful...

Thanks a lot in advance

with best regards

nikola ciprich

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