Subject: Re: [PATCH 5/5] mac80211: set NETIF_F_LLTX when using intermediate tx
 queues
To:     =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= <toke@redhat.com>,
        Felix Fietkau <nbd@nbd.name>, linux-wireless@vger.kernel.org
Cc:     johannes@sipsolutions.net, Herbert Xu <herbert@gondor.apana.org.au>
References: <20190316170634.13125-1-nbd@nbd.name>
 <20190316170634.13125-5-nbd@nbd.name> <87sgvmvg9g.fsf@toke.dk>
From:   Arend Van Spriel <arend.vanspriel@broadcom.com>
Message-ID: <773e4dff-29fd-22b4-e4bc-cd5a94c66dc2@broadcom.com>
Date:   Sun, 14 Apr 2019 11:44:17 +0200
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+ Herbert

On 3/16/2019 7:14 PM, Toke Høiland-Jørgensen wrote:
> Felix Fietkau <nbd@nbd.name> writes:
> 
>> When using iTXQ, tx sequence number allocation and statistics are run at
>> dequeue time. Because of that, it is safe to enable NETIF_F_LLTX, which
>> allows tx handlers to run on multiple CPUs in parallel.
> 
> Cool, didn't know about that flag.

It is water under the bridge as this patch got applied already, but I 
stumbled upon it just recently and didn't know about that flag either. 
So I looked for more information about it and found the definition [1], 
but the comment seemed important enough to send this reply.

	NETIF_F_LLTX_BIT,	/* LockLess TX - deprecated. Please */
				/* do not use LLTX in new drivers */

Here is the commit that marked it deprecated:

commit e24eb521fbf2a350ce879dfc1d8e56d4ffa2aa22
Author: Christian Borntraeger <borntraeger@de.ibm.com>
Date:   Tue Sep 25 19:42:02 2007 -0700

     [NET]: note that NETIF_F_LLTX is deprecated

So I am not sure we should really do this in mac80211. Maybe Herbert can 
comment although it has been over a decade ago.

Regards,
Arend

[1] 
https://elixir.bootlin.com/linux/latest/source/include/linux/netdev_features.h#L32