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

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Message-ID: <4D653C9C.8010205@trash.net>
Date:	Wed, 23 Feb 2011 17:58:04 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
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

Am 23.02.2011 17:48, schrieb Eric Dumazet:
> 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.

Yeah, but we might decrement buckets of different flows which
are non-zero. Probably not too bad, but still not correct.

> I had this idea (of storing two bits per skb), but :
> 
> - It means that swap_buffer() should not touch (bzero) the 'old' bins

Yes, it means we have to properly decrement the old buffer
until all bins reached zero.

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

Indeed.
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