[c-nsp] Stackwise 3750 and buffers

[Peter Rathlev]

On Mon, 2007-12-17 at 13:10 +0100, Peter Rathlev wrote:
> Also, I can try to adjust the buffers (global config "buffers big
> permanent <number>") but I am unanware of the consequenses of this. Will
> the switches tell me when they don't have enough RAM for the amount of
> buffers I try to reserve, or will they just start to perform very badly?

I tested this, and the switch tells me if it doesn't have the required
I/O-memory:

! Switch(config)#buffers huge permanent 500
! Switch(config)#
! 03:02:32: %SYS-2-MALLOCFAIL: Memory allocation of 18184 bytes 
! failed from 0x26C050, alignment 8 
! Pool: I/O  Free: 26216  Cause: Memory fragmentation 
! Alternate Pool: None  Free: 0  Cause: No Alternate pool 
! 
! -Process= "Exec", ipl= 6, pid= 84
! -Traceback= 8A4200 BE9EFC BEDBA8 26C054 271414 275394 275990 27568C 
! 852DDC 86D5D4 7599A8 7      
! Switch(config)#
! Switch(config)#do sh run | incl buff
! buffers small permanent 138
! buffers middle permanent 133
! buffers big permanent 858
! buffers big max-free 858
! buffers verybig permanent 33
! buffers huge permanent 500
! buffers huge max-free 12
! Switch(config)#do sh mem
!                 Head Total(b)  Used(b)  Free(b) Lowest(b) Largest(b)
! Processor    17C2A08 96720376 25383960 71336416  69201800   69467208
!       I/O    7400000 12574720 12548504    26216     26216      12208
<snip>

I can also see that the switch stack master tries to reserve the buffers
and stops when reaching 63, but that the command is not executed on the
other stack members.

Regarding buffer tuning, Cisco has the
http://www.cisco.com/warp/public/63/buffertuning.html document, but it
only describes buffer tuning for routers. At least I can see that a 3750
uses I/O-memory for buffers, and thus looks like the higher end routers.
But that's probably an oversimplification. :-)

Regards,
Peter Rathlev