netdev - Re: [patch net-next v2 10/11] act_police: improved accuracy at high rates

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Message-ID: <20130208221608.GA1516@minipsycho.orion>
Date:	Fri, 8 Feb 2013 23:16:08 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Eric Dumazet <eric.dumazet@...il.com>
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 v2 10/11] act_police: improved accuracy at high
 rates

Fri, Feb 08, 2013 at 08:12:35PM CET, eric.dumazet@...il.com wrote:
>On Fri, 2013-02-08 at 19:59 +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.
>> 
>> This is a followup to 56b765b79e9a78dc7d3f8850ba5e5567205a3ecd
>> 
>> Signed-off-by: Jiri Pirko <jiri@...nulli.us>
>> ---
>>  net/sched/act_police.c | 119 +++++++++++++++++++++++--------------------------
>>  1 file changed, 57 insertions(+), 62 deletions(-)
>> 
>> diff --git a/net/sched/act_police.c b/net/sched/act_police.c
>> index 378a649..8723183 100644
>> --- a/net/sched/act_police.c
>> +++ b/net/sched/act_police.c
>> @@ -26,20 +26,19 @@ struct tcf_police {
>>  	struct tcf_common	common;
>>  	int			tcfp_result;
>>  	u32			tcfp_ewma_rate;
>> -	u32			tcfp_burst;
>> +	s64			tcfp_burst;
>>  	u32			tcfp_mtu;
>> -	u32			tcfp_toks;
>> -	u32			tcfp_ptoks;
>> +	s64			tcfp_toks;
>> +	s64			tcfp_ptoks;
>>  	psched_time_t		tcfp_t_c;
>> -	struct qdisc_rate_table	*tcfp_R_tab;
>> -	struct qdisc_rate_table	*tcfp_P_tab;
>> +	struct psched_ratecfg	rate;
>> +	bool			rate_present;
>> +	struct psched_ratecfg	peak;
>> +	bool			peak_present;
>>  };
>>  #define to_police(pc)	\
>>  	container_of(pc, struct tcf_police, common)
>>  
>> -#define L2T(p, L)   qdisc_l2t((p)->tcfp_R_tab, L)
>> -#define L2T_P(p, L) qdisc_l2t((p)->tcfp_P_tab, L)
>> -
>>  #define POL_TAB_MASK     15
>>  static struct tcf_common *tcf_police_ht[POL_TAB_MASK + 1];
>>  static u32 police_idx_gen;
>> @@ -123,10 +122,6 @@ static void tcf_police_destroy(struct tcf_police *p)
>>  			write_unlock_bh(&police_lock);
>>  			gen_kill_estimator(&p->tcf_bstats,
>>  					   &p->tcf_rate_est);
>> -			if (p->tcfp_R_tab)
>> -				qdisc_put_rtab(p->tcfp_R_tab);
>> -			if (p->tcfp_P_tab)
>> -				qdisc_put_rtab(p->tcfp_P_tab);
>>  			/*
>>  			 * gen_estimator est_timer() might access p->tcf_lock
>>  			 * or bstats, wait a RCU grace period before freeing p
>> @@ -154,7 +149,6 @@ static int tcf_act_police_locate(struct net *net, struct nlattr *nla,
>>  	struct nlattr *tb[TCA_POLICE_MAX + 1];
>>  	struct tc_police *parm;
>>  	struct tcf_police *police;
>> -	struct qdisc_rate_table *R_tab = NULL, *P_tab = NULL;
>>  	int size;
>>  
>>  	if (nla == NULL)
>> @@ -197,21 +191,37 @@ static int tcf_act_police_locate(struct net *net, struct nlattr *nla,
>>  	if (bind)
>>  		police->tcf_bindcnt = 1;
>>  override:
>> +	spin_lock_bh(&police->tcf_lock);
>> +	police->tcfp_mtu = parm->mtu;
>> +	police->rate_present = false;
>> +	police->peak_present = false;
>>  	if (parm->rate.rate) {
>> +		struct qdisc_rate_table *tab;
>> +
>>  		err = -ENOMEM;
>> -		R_tab = qdisc_get_rtab(&parm->rate, tb[TCA_POLICE_RATE]);
>> -		if (R_tab == NULL)
>> -			goto failure;
>> +		tab = qdisc_get_rtab(&parm->rate, tb[TCA_POLICE_RATE]);
>
>This patch was not tested, it cannot possibly work
>
>spin_lock_bh();
>rtab = kmalloc(sizeof(*rtab), GFP_KERNEL);
>
>should crash or complain loudly.


Thanks, you are right, I had this debug option disabled. Will repost.

>
>
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