[c-nsp] GSR CPU Process is very HIGH 95%

[e ninja]

On Wed, Oct 7, 2009 at 2:01 PM, Lasher, Donn <DLasher at newedgenetworks.com>wrote:

> -----Original Message-----
> From: Pete Templin [mailto:petelists at templin.org]
> Subject: Re: [c-nsp] GSR CPU Process is very HIGH 95%
>
> Lasher, Donn wrote:
>
> >> To clarify, this depends on both the card type (engine 0/1/2/3/4/5)
> and
> >> traffic type (mpls, DSCP marking, etc).  You can be doing everything
> >> right, and still have 50% CPU with the wrong combination of those
> two..
> >> (For example, MPLS Labeling and Engine0 GIG-E card at 100M of
> traffic)
>
> >Right, but that'd be 50% CPU on the linecard, not on the xRP, right?
> >
> >(In other words, you'd find 50% CPU by doing 'execute-on all sh proc c
> s
> >| e 0.0.%' but wouldn't find it by doing 'sh proc c s | e 0.0.%'.)
>
> No, in the example I gave, 100M of CE-PE MPLS traffic (IE the router is
> labeling/unlabeling) on an Engine0 1-port GIG-E line card will run the
> Processor CPU up nice and high.


*That is because an Eng 0 LC switches traffic in software i.e. the LC CPU
does each and every lookup off the LC FIB table ( a rather CPU intensive
activity - at....you guessed it, LC CPU "interrupt level") - which was
downloaded as normal from the RP FIB table.

(GSR Architecture in four bullet points)

The GSR (and most distributed platforms are designed as follows...
*

   - *RP takes care of coalescing routes, creating FIB tables and all other
   housekeeping activities.*
   - *RP pushes FIB table down to all LCs and IOS 'inconsistency checker'
   runs every so often to ensure the 'consistency' of RP and LC copies of FIB
   tables et al.
   *
   - *If LC has hardware switching capabilities (i.e. > Eng 1)...yipppe. It
   switches packets in HW (ASIC) or else...*
   - *It switches in software i.e. LC CPU 'manually' does the CEF table
   lookup for each and every packet header - very CPU intensive. However, if,
   for some strange reason, a route doesn't exists on LC CEF table, the LC will
   punt to RP CPU. And RP will the final say on what happens to the packet.
   *

**
Eninja