[dpdk-dev] [PATCH v2] lib/librte_meter: fix divide by zero for RFC4115 meter
Dumitrescu, Cristian
cristian.dumitrescu at intel.com
Thu Feb 28 19:50:41 CET 2019
Hi Eelco,
Sorry for my delayed reply,
> -----Original Message-----
> From: Eelco Chaudron [mailto:echaudro at redhat.com]
> Sent: Friday, February 1, 2019 4:07 PM
> To: Dumitrescu, Cristian <cristian.dumitrescu at intel.com>
> Cc: dev at 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 at redhat.com
>
> Signed-off-by: Eelco Chaudron <echaudro at 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
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