netdev - Re: [PATCH net v7 1/2] net: sched: tbf: fix the calculation of max

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Date:	Wed, 11 Dec 2013 11:38:40 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yang Yingliang <yangyingliang@...wei.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, brouer@...hat.com,
	jpirko@...hat.com, jbrouer@...hat.com
Subject: Re: [PATCH net v7 1/2] net: sched: tbf: fix the calculation of
 max_size

On Tue, 2013-12-10 at 14:59 +0800, Yang Yingliang wrote:
> Current max_size is caluated from rate table. Now, the rate table
> has been replaced and it's wrong to caculate max_size based on this
> rate table. It can lead wrong calculation of max_size.
> 
> The burst in kernel may be lower than user asked, because burst may gets
> some loss when transform it to buffer(E.g. "burst 40kb rate 30mbit/s")
> and it seems we cannot avoid this loss. Burst's value(max_size) based on
> rate table may be equal user asked. If a packet's length is max_size, this
> packet will be stalled in tbf_dequeue() because its length is above the
> burst in kernel so that it cannot get enough tokens. The max_size guards
> against enqueuing packet sizes above q->buffer "time" in tbf_enqueue().
> 
> To make consistent with the calculation of tokens, this patch add a helper
> psched_ns_t2l() to calculate burst(max_size) directly to fix this problem.
> 
> After this fix, we can support to using 64bit rates to calculate burst as well.
> 
> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> ---

Acked-by: Eric Dumazet <edumazet@...gle.com>


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