From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next-2.6 v3] net_sched: SFB flow scheduler
Date: Wed, 23 Feb 2011 17:48:31 +0100
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Cc: David Miller <davem@davemloft.net>,
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To: Patrick McHardy <kaber@trash.net>
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Le mercredi 23 f=C3=A9vrier 2011 =C3=A0 17:24 +0100, Patrick McHardy a =
=C3=A9crit :

> This needs to be a per-skb property, otherwise you could have the
> situation:
>=20
> - enqueue skb, double_buffering=3D0, increment buffer 0
> - enable double buffering
> - swap buffers
> - dequeue same skb, decrement buffer 1
>=20
> after which the qlen values of buffer 1 will be incorrect.
>=20

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).


>=20
> > +		slot ^=3D 1;
> > +		sfbhash =3D sfb_hash(skb, slot, q);
>=20
> 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 !