Re: [PATCH 1/3] kvm tools: Make virtio-net kvm__irq_line thread safe

[Sasha Levin <levinsasha928@gmail.com>]

On Fri, 2011-04-29 at 12:22 +0200, Ingo Molnar wrote:
> If that is so then indeed the right approach might be to signal the guest every 
> time we manage to readv() something - there might not come any other packet for 
> a long time. But the reason is not some 'erroneous state' - all state is 
> perfectly fine, this is simply a basic property of the event loop that the rx 
> thread implements ...

My idea as for 'erroneous state' was as follows:

We have 2 virt queues: one for RX and one for TX, each on it's own
thread.

RX Thread:
 - Runs readv() and reads data.
 - Calls virt_queue__set_used_elem() which starts updating the RX virt
queue.

TX Thread:
 - Runs readv() and reads data.
 - Calls and returns from virt_queue__set_used_elem().
 - Calls kvm__irq_line().

At this point, The RX queue state is being updated but since the IRQ was
signaled (same IRQ for both TX and RX) the guest virtio-net checks the
RX queue and finds a virt queue that wasn't fully updated.

-- 

Sasha.