> From: Jesper Skriver [mailto:jes...@skriver.dk]
> Sent: Tuesday, November 03, 2015 10:34 AM
>
> On Mon, Nov 02, 2015 at 06:30:00PM +0000, Adam Vitkovsky wrote:
> >
Adam Vitkovsky
IP Engineer
T: 0333 006 5936
E: adam.vitkov...@gamma.co.uk
W: www.gamma.co.uk
This is an email from Gamma Telecom Ltd, trading as “Gamma”. The contents of
this email are confidential to the ordinary user of the email address to which
it was addressed. This email is not intended to create any legal relationship.
No one else may place any reliance upon it, or copy or forward all or any of it
in any form (unless otherwise notified). If you receive this email in error,
please accept our apologies, we would be obliged if you would telephone our
postmaster on +44 (0) 808 178 9652 or email postmas...@gamma.co.uk
Gamma Telecom Limited, a company incorporated in England and Wales, with
limited liability, with registered number 04340834, and whose registered office
is at 5 Fleet Place London EC4M 7RD and whose principal place of business is at
Kings House, Kings Road West, Newbury, Berkshire, RG14 5BY.
-----Original Message-----
> > > From: Jesper Skriver [mailto:jes...@skriver.dk]
> > > Sent: Monday, November 02, 2015 5:14 PM
> > >
> > >
> > > Right, on those types of platforms it can be done - assuming there
> > > are spare bits in the meta data that goes with the packet, enough
> > > free instruction space etc - but it will come at a performance
> > > impact as it will require more cycles per packet, unless on the
> > > particular platform there is still headroom for adding more cycles without
> affecting the ability to be linerate ...
> >
> > Talking about lookup performance isn't the number of cycles negligible
> compared to memory access times please?
>
> Different architectures behave differently, but if you can arrange the new
> data such that it will fit the same cache line as data you are already
> reading,
> the additional read of the new data will come from the CPU data cache, and
> is typically very fast. You are right an uncached read is often 100's of
> instructions.
>
Just to make sure I mean the memory access to perform the Trie lookup in the
SDRAM/SRAM/DRAM (not the instructions -which I agree is very important to fit
into the on Chip memory).
Although I see there are several options on how to accomplish multiple read
operations per cycle which makes the features coupling non-deterministic with
regards to lookup performance.(like next-table vs FBF, I'm pretty sure
next-table needs two lookups where FBF only needs one yet both have the same
performance impact).
Please let me know your thoughts.
> > Even the high-end platforms of all vendors will cripple performance when
> features are enabled.
>
> Some more than others ...
>
I agree, I guess it all boils down to how mem-lookup efficient the lookup algo
is and of course on how many read operations per cycle can be done.
What do you think?
> > > Which is why I in my original reply said that it would not be
> > > practical. For it to be useful all routers in the path needs to
> > > support it, otherwise as soon as it hits one that doesn't all the
> > > various MPLS sub-types will get mixed together again.
> > > Features which require network wide support are quite hard to get
> > > off the ground.
> >
> > Maybe this could get shoehorned along with segment routing.
>
> Doubt it, SR specifications are very far along, and several vendors have
> working implementations.
>
Yeah I guess that ship has sailed a long time ago.
But I like your example with the Entropy label.
What if the topmost label value or even better the VPN/VC label could indicate
how to parse the remainder of the packet.
And if a middle node or end node(in case of a VPN/VC label) doesn't understand
the encoding it would just label switch the packet blindly.
It should be very simple to implement and also to adjust the label-space so
that it doesn't conflict with anything else
So all nodes that support the feature would start allocating with:
847.... MPLS-UNSPECIFIED
848.... MPLS-IP
849.... MPLS-ETH
And so forth..
adam
_______________________________________________
juniper-nsp mailing list juniper-nsp@puck.nether.net
https://puck.nether.net/mailman/listinfo/juniper-nsp
