Re: [dpdk-dev] [PATCH v2] lib/librte_meter: fix divide by zero for RFC4115 meter

["Eelco Chaudron" <echaudro@redhat.com>]

On 28 Feb 2019, at 19:50, Dumitrescu, Cristian wrote:

> Hi Eelco,
>
> Sorry for my delayed reply

No problem I was OOO also so hence my late reply ;)

>> -----Original Message-----
>> From: Eelco Chaudron [mailto:echaudro@redhat.com]
>> Sent: Friday, February 1, 2019 4:07 PM
>> To: Dumitrescu, Cristian <cristian.dumitrescu@intel.com>
>> Cc: dev@dpdk.org
>> Subject: [PATCH v2] lib/librte_meter: fix divide by zero for RFC4115 
>> meter
>>
>> RFC 4115 allows a meter with either cir and/or eir configured.
>> When only one is configured a divide by zero would occur.
>>
>> Fixes: 655796d2b5fb ("meter: support RFC4115 trTCM")
>> Cc: echaudro@redhat.com
>>
>> Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
>> ---
>>
>>  v2 - Removed configuration change that got included by accident
>>
>>  lib/librte_meter/rte_meter.h |    8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/lib/librte_meter/rte_meter.h 
>> b/lib/librte_meter/rte_meter.h
>> index 005e4eeee..56d85ecf0 100644
>> --- a/lib/librte_meter/rte_meter.h
>> +++ b/lib/librte_meter/rte_meter.h
>> @@ -597,8 +597,8 @@ rte_meter_trtcm_rfc4115_color_blind_check(
>>  	/* Bucket update */
>>  	time_diff_tc = time - m->time_tc;
>>  	time_diff_te = time - m->time_te;
>> -	n_periods_tc = time_diff_tc / p->cir_period;
>> -	n_periods_te = time_diff_te / p->eir_period;
>> +	n_periods_tc = p->cir_period != 0 ? time_diff_tc / p->cir_period : 
>> 0;
>> +	n_periods_te = p->eir_period != 0 ? time_diff_te / p->eir_period : 
>> 0;
>>  	m->time_tc += n_periods_tc * p->cir_period;
>>  	m->time_te += n_periods_te * p->eir_period;
>>
>> @@ -641,8 +641,8 @@ rte_meter_trtcm_rfc4115_color_aware_check(
>>  	/* Bucket update */
>>  	time_diff_tc = time - m->time_tc;
>>  	time_diff_te = time - m->time_te;
>> -	n_periods_tc = time_diff_tc / p->cir_period;
>> -	n_periods_te = time_diff_te / p->eir_period;
>> +	n_periods_tc = p->cir_period != 0 ? time_diff_tc / p->cir_period : 
>> 0;
>> +	n_periods_te = p->eir_period != 0 ? time_diff_te / p->eir_period : 
>> 0;
>>  	m->time_tc += n_periods_tc * p->cir_period;
>>  	m->time_te += n_periods_te * p->eir_period;
>>
>
> Yes, this is indeed an issue, good catch!
>
> For performance reasons, we'd like to avoid a test on the fast path 
> (rte_meter_xyz_check) and replace it with more work done on the 
> configuration stage (rte_meter_profile_xyz_config), if possible.
>
> We can intercept the null CIR or EIR cases very early in 
> rte_meter_trtcm_rfc4115_profile_config() and deal with them separately 
> by setting the CIR/EIR period and bytes_per_period to some neutral 
> values and skipping the call to rte_meter_get_tb_params(): period = 
> RTE_METER_TB_PERIOD_MIN, bytes_per_period = 0.

Excellent idea, will sent out a v3 soon, after some testing…

//Eelco