Re: [PATCH] zd1211rw-mac80211: limit URB buffering in tx path

On Tue, 1 May 2007 21:50:08 +0200, Ulrich Kunitz wrote:

On 07-05-01 12:34 Jiri Benc wrote:

quoted

On Tue,  1 May 2007 04:01:00 +0100 (BST), Daniel Drake wrote:

quoted

The old code allowed unlimited buffing of tx frames in URBs
submitted for transfer to the device. This patch stops the
ieee80211_hw queue(s) if to many URBs are ready for submit to the
device. Actually the ZD1211 device supports currently only one
queue.

This doesn't look correct to me. The limits should be per queue and you
should always stop queues selectively.

The old ZD1211 chip doesn't support queuing and the new ZD1211B
chip has support, but it is unclear how to put packets in the
different queues. However the error condition here is, that
packets can't be transmitted over the USB, which will affect all
queues.

Really? From what you wrote ("if too many URBs are ready for submit") it
seems that the code is triggered when the queue is just full. That's not
necessarily an error condition and the only thing needed to do is to stop
the queue. Unless zd1211 is really special here (and then I'd like to know
how is it special).

Sure one could manage different high level marks for the
different queues, but this is all theoretical currently. I could
have coded with the explicit knowledge that we support only one
queue, but it is really work the hassle.

If you support one queue only, call ieee80211_stop_queue(hw, 0). Calling
ieee80211_stop_queues if you have just a full queue is wrong.

Thanks,

 Jiri

-- 
Jiri Benc
SUSE Labs