Re: [PATCH 0/11] RFC: PCI using capabilitities

[Sasha Levin <levinsasha928@gmail.com>]

On Sun, 2011-12-11 at 14:47 +0200, Michael S. Tsirkin wrote:
> First, I'd like to answer your questions from the PCI side.
> Look for PCI rules in the PCI spec.
> You will notices that a write is required to be able to
> pass a read request. It might also pass read completion.
> A read request will not pass a write request.
> There's more or less no ordering between different types of transactions
> (memory versus io/configuration).
> 
> That's wrt to the question you asked.
> 
> But this is not your setup: you have a single vcpu so
> you will not initiate a write (select vq) until you get
> a read completion.
> 
> So what you are really describing is this setup: guest reads a value,
> gets the response, then writes out another one, and kvm tool reports the
> write before the read. 

No, it's exactly the opposite. Guest writes a value first and then reads
one (writes queue_select and reads queue_address) and kvm tool reporting
the read before the write.

I must add here that the kvm tool doesn't do anything fancy with simple
IO/MMIO. Theres no thread games or anything similar there. The vcpu
thread is doing all the IO/MMIO work.

-- 

Sasha.