netdev - Re: [PATCH] net: Add batman-adv meshing protocol

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Date:	Tue, 20 Jul 2010 10:28:10 +0200
From:	Sven Eckelmann <sven.eckelmann@....de>
To:	b.a.t.m.a.n@...ts.open-mesh.org,
	Simon Wunderlich <siwu@....tu-chemnitz.de>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: Add batman-adv meshing protocol

Thanks a lot for your review and for your hints.

David Miller wrote:
> From: Sven Eckelmann <sven.eckelmann@....de>
> Date: Fri, 16 Jul 2010 16:39:16 +0200
[...]
> 
> The kernel has a hamming weight library function which takes advantage
> of population count instructions on cpus that suport it, and also has
> a sw version than is faster than what you're doing here, please use
> it.
> 
> The interfaces are called "hweight{8,16,32,64}()" where the number in
> the name indicates the bit-size of the word the interface operates on.

Correct, the inner loop is a quite straight forward implementation without any 
kind of optimization. I will change that.

> I also notice that this code uses it's own internal buffering scheme
> with kmalloc()'d buffers, then seperately allocates actual SKB's and
> copies the data there.
> 
> Just use the SKB facilities how they were designed to be used, instead
> of needlessly inventing new things.  Allocate your initial SKB and put
> the initial forwarding header in it, then when you want to send a copy
> off, skb_clone() it, and push the other bits you want at the head
> and/or the tail of the cloned SKB, then simply send it off.

Good catch. That comes from a time when batman-adv was a minimalistic 
conversation of the userspace proof of concept implementation. This happens 
for example in vis.c, icmp_socket.c and send.c (just grepping for 
send_raw_packet is a good way to find those places). But is also happening 
with batman_if->packet_buff in schedule_own_packet and similar places.

I would leave that to the original author of those functions.

thanks,
	Sven

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