netdev - Re: [patch net-next v3 10/11] act_police: improved accuracy at high rates

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Message-ID: <1360460027.20362.4.camel@edumazet-glaptop>
Date:	Sat, 09 Feb 2013 17:33:47 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	jhs@...atatu.com, kuznet@....inr.ac.ru, j.vimal@...il.com
Subject: Re: [patch net-next v3 10/11] act_police: improved accuracy at high
 rates

On Sat, 2013-02-09 at 17:45 +0100, Jiri Pirko wrote:
> Current act_police uses rate table computed by the "tc" userspace program,
> which has the following issue:
> 
> The rate table has 256 entries to map packet lengths to
> token (time units).  With TSO sized packets, the 256 entry granularity
> leads to loss/gain of rate, making the token bucket inaccurate.
> 
> Thus, instead of relying on rate table, this patch explicitly computes
> the time and accounts for packet transmission times with nanosecond
> granularity.
> 

...


> -			ptoks -= L2T_P(police, qdisc_pkt_len(skb));
> +			if (ptoks > (s64) psched_l2t_ns(&police->peak,
> +							police->tcfp_mtu))
> +				ptoks = (s64) psched_l2t_ns(&police->peak,
> +							    police->tcfp_mtu);

Same remark here, this should be in a cached variable.

> +			ptoks -= (s64) psched_l2t_ns(&police->peak,
> +						     qdisc_pkt_len(skb));
>  		}


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