netdev - Re: Another try at getting pktgen to work with wifi.

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Date:	Fri, 31 May 2013 20:41:38 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Ben Greear <greearb@...delatech.com>
Cc:	Felix Fietkau <nbd@...nwrt.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Another try at getting pktgen to work with wifi.

On Fri, 2013-05-31 at 11:00 -0700, Ben Greear wrote:

> I think it might be more that the wifi stacks have some specific
> assumptions about how skb->priority maps to queues and QoS.  If
> they get out of sync, then the TID mappings and so forth get
> confused.

What I'm saying though is that I don't see where skb->priority is even
_used_ in the wifi stack. I can see it getting set, but not used.

> I actually don't know exactly why pktgen shows this problem,
> but it must be because it does direct calls to the hard_start_xmit
> method of the netdev when (most?) other paths do dev_queue_xmit
> or similar.

Other paths go through select_queue(), obviously.

> > Actually that makes it seem like something else should be doing packet
> > classification, not mac80211 in select_queue()?
> >
> > Where is skb->priority actually really used in mac80211? I don't see
> > much?
> 
> There's a bit more in net/wireless/util.c, at least (cfg80211_classify8021d, for instance).

But that's pretty much all assignments.

> The mac80211/wme.c uses it.  Some of this is called from the drivers
> (line 1916 or so of ath9k/xmit.c).

What's called there? I don't see any reason for that to use
skb->priority?

> It's all a bit convoluted in my opinion, but there may well
> be good reasons for it.

More likely legacy.

johannes

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