Re: qemu pcnet emulation problems.

[Nivedita Singhvi <niv@us.ibm.com>]

Don Fry wrote:
> There are/may be several other bugs with the qemu pcnet emulation.  I do

Not sure if Don mentioned this earlier, but for the benefit of those
who might need the context, please see Xen Bugzilla #574/#575.

> not know if there is any other serialization outside of this code, but if
> both a transmit and a receive operation were to be performed at the same
> time on different cpus, since the same buffer is used for both transmit
> and receive, that would also cause data corruption.
> 
> Does anyone else know how this is prevented, or is this another source
> of corruption?
> 
> Another thing I noticed, that will reduce throughput if corrected, is
> that the wrong bit is being examined in the receive path, to determine
> if mac level crc should be computed.  Right now, the wrong bit is being
> checked and no mac level crc is being calculated.  If the right bit were
> looked at, mac level crc would need to be computed, slowing down the
> transfers.  However, since no driver cares about the crc right now,
> since neither Linux or XP complain, could the code to compute the crc be
> deleted?  Maybe just comment that the crc should be computed.
> 
> Any recommendations?

I'd really like to continue to avoid the CRC computation between
domains, but intentionally, this time, in a clean way :).

thanks,
Nivedita