Re: Route cache performance under stress

On Mon, 19 May 2003, David S. Miller wrote:

I found a description of this thing on Cisco's web site.  Amusingly it
seems to contradict itself, it says that the CEF FIB is fully
populated and has a 1-to-1 correspondance to the routing table yet it
says that the first access to some destination is what creates
CEF entries.

It seems to be done at interupt level sort of like Linux fast switching
(not to be confused with CISCO fast switching); however, unlike Linux fast
switching which looks up based on dst cache, they do lookups on a
FIB with already nexthop entries (sort of like the hh cache we have).
Theres something akin to a user land process which makes sure the
neighbors are resolved all the time - most routing protocols stacks
already do this today with BGP. I dont think Zebra does.
What i am wondering is what if they have to do more than routing? Dont
they end up with same (if not worse) effect?

Having said all the above, i think it would be worth seeing what the
effect of improving the slow path is (make it a multi-way trie).
Actually before that someone needs to prove slow path is slow ;->
Note: It may make sense that we have options to totaly remove
the cache lookups if necessary - noone has proved a need for it at this
point.

cheers,
jamal