[nsp] Cisco 3550 I/O memory fragmentation problem

[Łukasz Bromirski]

Hi,

Did anyone else hit the problem with the 3550-12T switches, regarding the
I/O memory fragmentation?

I've got a client, that uses one 3550-12T as a core switch. It requires
running OSPF, few ports as a switchports and two ports as a L3 IP interfaces.
That's where the problem begins.

One of the L3 interfaces is capable of receiving bursts of ~1500-bytes
frames, causing MALLOCFAIL messages and interface flapping (down/up/down/up).

The messages are like that:

%SYS-2-MALLOCFAIL: Memory allocation of 1680 bytes failed from
   0x156550, alignment 0
Pool: I/O  Free: 2172  Cause: Memory fragmentation

And I/O memory buffers are washed out:

show memory summary (after ~3 hours):

               Head Total(b)  Used(b)   Free(b) Lowest(b)  Largest(b)
Processor   BDDF8C 54655092  4842004  49813088  47010552    47973440
       I/O 80000000  8388608  1128084   7260524      2172     7187568

...notice the "Lowest(b)" column on I/O. The `show buffers' command gives:

show buffers:
[...]
Big buffers, 1524 bytes (total 143, permanent 128, peak 4356 @ 3h):
      135 in free list (128 min, 512 max allowed)
      1908668 hits, 137710 misses, 62727 trims, 62742 created
      4196 failures (3616 no memory)

So I did some buffer tuning, but I'm almost sure, that the next burst will
still cause memory fragmentation and interface flapping.

What I'm looking, is some way to change I/O memory allocation (I know
that `memory-size' iomem doesn't work on this platform) or someone, who has
similar 3550-12T and can say "Whoa, I occasionally hit low I/O but my
interfaces stay up all the time".

Thanks,
-- 
Łukasz Bromirski                             lbromirski:mr0vka,eu,org