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

["Dumitrescu, Cristian" <cristian.dumitrescu@intel.com>]

Hi Eelco,

Sorry for my delayed 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.

Makes sense?

Regards,
Cristian