netdev - Re: [PATCH net-next-2.6 v3] net

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Date:	Wed, 23 Feb 2011 17:48:31 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	David Miller <davem@...emloft.net>,
	Juliusz Chroboczek <Juliusz.Chroboczek@....jussieu.fr>,
	"John W. Linville" <linville@...driver.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	netdev <netdev@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH net-next-2.6 v3] net_sched: SFB flow scheduler

Le mercredi 23 février 2011 à 17:24 +0100, Patrick McHardy a écrit :

> This needs to be a per-skb property, otherwise you could have the
> situation:
> 
> - enqueue skb, double_buffering=0, increment buffer 0
> - enable double buffering
> - swap buffers
> - dequeue same skb, decrement buffer 1
> 
> after which the qlen values of buffer 1 will be incorrect.
> 

Normally its OK, because we bzero() the zone, and the "decrement" is
0-bounded.

I had this idea (of storing two bits per skb), but :

- It means that swap_buffer() should not touch (bzero) the 'old' bins

- Since hash perturbator is changed, we have to store the two hash
values per skb (instead of one u32 / classid).


> 
> > +		slot ^= 1;
> > +		sfbhash = sfb_hash(skb, slot, q);
> 
> Isn't there room in the cb to store both hash values?

Yes, I am going to implement your idea, its probably OK to use two u32
on skb_cb for this.

Thanks !


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