[geeks] Gb interface for Ultra-30

[Peter L. Wargo]

On Friday, February 15, 2002, at 05:41 , Kurt Huhn wrote:

>> Keep in mind that Sun generally doesn't recommend gbit ether on
>> lower-speed single-cpu systems.  (it'll work, but puts a high load on a
>> CPU.)
>
> Really?  Why's that?

In most microprocessor-centric systems, the I/O is *not* divorced from 
the cpu - there are I/O cards out there with some level of intelligence, 
but usually the CPU has some pretty heavy involvement in the I/O 
process, especially on the network transport side.  So, a cpu that's 
happy handling 100mbit may be a bit taxed at 10x that rate. (Remember, 
gigabit is roughly 100 megabytes/sec.)

Even 100mbit puts a load on a CPU - fire up perfbar or mpstat and watch 
it while you ftp a large file.  For example, here is 'mpstat 1' output 
from an otherwise idle Ultra1/200E when I ftp a rather large 
(78954240byte) file:

   0    0   0    0   418  218   48    0    0    0    0    30    0   0   0 
100
   0    5   0    0   611  408  159    4    0    1    0   218    1   8   
0  91
   0    0   0    0   853  642  531    6    0    5    0   694    0  20   
0  80
   0    0   0    0   863  653  520    7    0    4    0   690    0  20   
0  80
   0    0   0    0   852  642  541   13    0    5    0   692    0  17   
0  83
   0    0   0    0   851  641  511    2    0    0    0   682    1  23   
0  76
   0    0   0    0   849  639  510    6    0    3    0   670    0  26   
0  74
   0    0   0    0   864  654  528    6    0    2    0   761    1  17   
0  82
   0    0   0    0   796  586  458    8    0    2    0   601    1  18   
0  81
   0    0   0    0   865  654  503    6    0    1    0   693    0  23   
0  77
   0    0   0    0   850  640  507    5    0    1    0   680    0  21   
0  79
   0    0   0    0   839  629  504    6    0    4    0   662    0  24   
0  76
   0    0   0    0   872  662  533    5    0    2    0   698    0  28   
0  72
   0  112   0    0   846  635  502    9    0    2    0   881    3  32   
1  64
CPU minf mjf xcal  intr ithr  csw icsw migr smtx  srw syscl  usr sys  wt 
idl
   0    0   0    0   841  631  515    6    0    3    0   682    0  31   
0  69
   0    0   0    0   858  647  505    7    0    2    0   679    1  33   
0  66
   0    3   0    0   869  660  480   12    0    3    0  1033    3  32  
20  45
   0    7   0    0   472  272   70    0    0    0    0   152    0   1  
14  85
   0    0   0    0   408  208   23    0    0    0    0    31    0   0   0 
100

If you average it out, It looks like there is about a 20-25% load on the 
CPU, and this is pushing an average of 5.5M/sec (according to the FTP 
results.)

You can see where it can lead.  This is one of the reasons why I prob. 
won't bother to get 100mbit cards for my older macs - kinda overkill for 
a 68030...

_pete