[j-nsp] What exactly causes inconsistent RTT seen using ping utility in Junos?

[Saku Ytti]

On Thu, 25 Apr 2019 at 00:19, Martin T <m4rtntns at gmail.com> wrote:

> in PFE) could indeed be affected. On the other hand, the overall LC
> CPU usage according to "sh linux cpu usage" did not exceed 80% even
> during the route churn, but I actually do not know what exactly this
> utilization means..

Like ethernet, CPU core is either busy (100%) or not busy (0%), and
load is looking some specific time frame and telling how often in that
time frame CPU was busy.
So 80% of time, work needed to compete for access to the CPU.

If I understood your explanation right (I may not have):

WireI => PFEi => RE => PFEe => WireE

You measure stable delay from WireI to PFEe even under load (so PFEi
is not contributing to jitter, neither is RE (running RPD)
contributing on either receive or send direction).
But you measure variant delay from WireI to WireE (so PFEe is largely
responsible of jitter)

So perhaps ingress side punt is done through LC CPU interrupt and
egress side is not, causing egress side to cause more jitter,
depending on what the egress PFE LC CPU is doing.

-- 
  ++ytti