On Wed, Jun 27, 2012 at 6:25 PM, Johannes Berg
[off-list ref] wrote:

On Wed, 2012-06-27 at 18:20 +0300, Arik Nemtsov wrote:

quoted

quoted

It'll depend on the driver I guess? If you're going to set a flag "give
this vif priority now" on the first invocation, then you probably
wouldn't care about the timing. It looks like our implementation would
actually start some "give me the channel" operation and when the
firmware says "ok you have the channel now" we'd return and rely on
getting the TX right after.

Wrt. the race, this isn't going to be something that happens within less
than a millisecond or so, it's going to give us maybe 50ms at least of
channel time (WFA mandates replying within 30ms), so that doesn't seem
like a problem?

It's probably not an issue. Just seems simpler to just give the skb to
the driver so it can do whatever it wants before/during/after. Bypass
op_tx completely for these.

Yeah, that was one of the other options I considered in my original
email ... but this call must be able to sleep, and the TX processing in
mac80211 cannot sleep, so unless we bypass all processing (which seems
wrong) that would be rather difficult to implement.

Good point. But another race to consider the the
multi-channel/multi-vif scenario, where the driver already has a lot
of packets queued up, so the time will expire before we get a chance
to Tx. Again this is not a problem in practice (since it's the VO ac).

How about somehow requiring a multi channel driver to give always
Tx-ack? That will mean we can abandon the retry timers, and rely on
the driver to give an answer within a reasonable time.