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

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Message-ID: <51A8F141.5050804@candelatech.com>
Date:	Fri, 31 May 2013 11:51:45 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	Johannes Berg <johannes@...solutions.net>
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 05/31/2013 11:41 AM, Johannes Berg wrote:
> 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.

ieee80211_downgrade_queue
wme_downgrade_ac // sort of
ieee80211_select_queue_80211 // sort of...seems twiddling skb->priority is more of a by-product here.

cfg80211_classify8021d

>>> 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.

cfg80211_classify8021d uses it to determine the queue in if skb->priority is
set to a special range (hard coded un-documented hack from hell, it appears).

I didn't go looking to find out where those magic values might be set.


>> 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?

Ok, I was confused about that..but that *is* the code that pukes if you
have have mis-matched queues like you get with pktgen in upstream kernels...

Thanks,
Ben


-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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