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Whats so difficult about ISSU

On (2012-11-09 13:33 -0500), Pete Lumbis wrote:

> I apologize, I realized I forgot a critical word in my reply.
> The new Cisco OSes are /NOT/ run to completion.

I did not notice that :). I assumed not was there, and was arguing that I
thought IOS XE still is. I know XR and NX-OS aren't.

> For IOS-XE we have Linux in charge of the scheduler with a
> multi-threaded IOSd process responsible for the control plane.  I'm

I'm sceptical if this means there isn't normal IOS run-to-completion
scheduler, certainly not all ios processes are separate threads to linux
kernel? But I guess this is moving target. Would be interesting to hear how
many threads, what are threads relative priorities, what runs in each
thread etc.
But anyhow just to hear it is threaded, is good news. Does this mean, IOSd
can capitalize on multiple cores? (Something JunOS cannot do today)

> critical IOSd process for example). The down side of this model is
> that control plane scaling, due to message passing, starts to have a
> lot of overhead. You can see this in the fact that the NX-OS routing
> scale is not where IOS-XE is.

Yup, luckily you guys stopped freescale pq3 and switch to xeon in ng nexus
sup (unfortunately you also killed CMP, which I think every vendor should
have). I think the overhead is worth it, built correctly you can scale
horizontally and just keep throwing faster RP CPU at it.