[j-nsp] Output queue drops and temporal buffers

[david.roy at orange.com]

Hi

We experienced unexpected drops with temporal buffer (which is a static buffer) and iCHIP based cards. It was in junos 11.4. Jtac had found an internal PR that matched our issue. 

Workaround was the using buffer-size in %. 

Which version and cards do you use? 

David

Envoyé de mon iPad

> Le 1 oct. 2013 à 21:13, "John Neiberger" <jneiberger at gmail.com> a écrit :
> 
> I've been troubleshooting an interesting problem off and on the past couple
> of days. We have a 1-gig link that is consistently running around 10%
> utilization, give or take a couple of percent, but we see periods where the
> egress WRED drops for queue 0 spike. It's bizarre because there is no
> corresponding increase in overall utilization. I don't know much about
> queueing on this platform (MX960), but I've been reading up on it today.
> Here is the config for that queue:
> 
> TRAFFIC-CLASS-1-SCHEDULER {
>    transmit-rate percent 20;
>    buffer-size temporal 50k;
>    priority low;
>    drop-profile-map loss-priority low protocol any drop-profile DROP-LOW;
>    drop-profile-map loss-priority high protocol any drop-profile DROP-HIGH;
> 
> As I understand it, the formula to determine available buffer space is this:
> 
> bandwidth * transmit-rate percent * temporal buffer size
> 
> On a 1-gig link, I think that means that queue has a total buffer size of
> 1.25 MB. I'm guessing that means that we must be getting large-ish chunks
> of data big enough to come close to filling that queue but intermittent
> enough that the average rate doesn't go up noticeably.
> 
> My question regarding the config is this: if we are already setting the
> transmit rate percentage, why would we also configure a temporal
> allocation? Isn't a percentage of the available bandwidth sufficient? What
> does adding a temporal allocation buy us? Is the transmit rate percent just
> setting how often that queue is serviced, while the buffer-size configures
> the queue depth?
> 
> Thanks,
> John
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