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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@kernel.org>
To:     Johannes Berg <johannes@sipsolutions.net>,
        Felix Fietkau <nbd@nbd.name>,
        Alexander Wetzel <alexander@wetzel-home.de>
Cc:     linux-wireless@vger.kernel.org
Subject: Re: [PATCH] mac80211: Simplify queue selection
In-Reply-To: <b900d560d5dabaea1a9faf9d8ff8a019ed813e25.camel@sipsolutions.net>
References: <20220510155828.9406-1-alexander@wetzel-home.de>
 <54589d98-882c-cee4-dd6d-140d50f400d0@nbd.name>
 <b900d560d5dabaea1a9faf9d8ff8a019ed813e25.camel@sipsolutions.net>
Date:   Tue, 10 May 2022 21:27:25 +0200
Message-ID: <87tu9xw5lu.fsf@toke.dk>
MIME-Version: 1.0
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Johannes Berg <johannes@sipsolutions.net> writes:

> On Tue, 2022-05-10 at 18:10 +0200, Felix Fietkau wrote:
>> On 10.05.22 17:58, Alexander Wetzel wrote:
>> > Let iTXQ drivers also register four queues in netdev and move queue
>> > assignment to ndo_select_queue(), like it's done for other drivers.
>> > 
>> > This gets rid of a special case in mac80211 and also increases the
>> > chance that when we call skb_get_hash() the skb is still hot in the CPU
>> > buffers.
>> > 
>> > Signed-off-by: Alexander Wetzel <alexander@wetzel-home.de>
>> 
>> This has the disadvantage of requiring a redundant sta lookup in the tx 
>> path for iTXQ drivers. I think the CPU cost of that one is probably 
>> higher than any potential gain from calling skb_get_hash a bit earlier.
>> 
>
> However, that's independent - we can still calculate the hash there, and
> then bail out, i.e. put it right before the "if (wake_tx_queue) return"
> part, no?
>
> OTOH we don't even need the hash in the other cases, do we?

Nope, that was my point on the "moving it to shared netdev core"
question :)

-Toke