[ale] Choke point (or when to bring on router)

[Bao C. Ha]

Hi Jeff,

The Linux kernel seem to have problems pushing packets above 
OC-12 ATM/Sonnet speed (622 Mbits/s).  Many people choose to 
move over to FreeBSD at this point.  But I think it should be
fixed rather easily.

The PCI bus is spec'ed at 133 MBytes/s.  A 64-bit version of
PCI would increase the bandwidth to twice of that.

My view is still that the backplane bandwidth of the PCI bus
is what limiting us.  For example, the high end Cisco 12000
can push giga and giga of bits.  Its Gigabit Route Processor
is a 200-Mhz R5000 Mips(?) processor.  It does have dedicated
ASICs.  A regular 700-Mhz Celeron would not have any problems
keeping up with it, though.

Bao

> >A 25-Mhz 486 can do a T1 or 2,3,4 T1s easily!  A T3 is only
> >45 Mbits/s full-duplex.  You will need to go to ATM/Sonnet
> >speeds before you will see a stall in Linux.
> >
> >A Cisco is better in pushing packets, not because its CPU
> >is faster, but rather its backplane can handle a lot more
> >bandwidth.  PCI is the bottleneck for PC-based high
> >speed transfers.
> >
> Is there a step up available regarding this PCI bottleneck?  
> Is 64-bit 
> PCI any help?  Are there even 64-bit-PCI-bus NICs?  If yes to 
> both, what 
> CPU options are there?  I'm just wondering where you go from 
> here if you 
> still want to avoid dedicated router HW but are running up 
> against the 
> PCI bus limit.


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