[Beowulf] Home beowulf - NIC latencies

[daniel.kidger at quadrics.com]

Duncan wrote (in reply to Patrick)
> > The good news is that you can pipeline it very well. 
> 
> Indeed. There is lots of parallelism in the hardware
> so you can me processing multiple requests at the same
> time. In this sequence of short jobs I measure the 
> average time for 8 byte gets 2 at a time, 4 at a time
> etc. 
> 
> quorumi: prun -N2 pgping -f get -b2 8
>   1:        8 bytes      1.32 uSec     6.07 MB/s
> quorumi: prun -N2 pgping -f get -b4 8
>   1:        8 bytes      1.04 uSec     7.66 MB/s
> quorumi: prun -N2 pgping -f get -b8 8
>   1:        8 bytes      0.84 uSec     9.47 MB/s
> quorumi: prun -N2 pgping -f get -b16 8
>   1:        8 bytes      0.82 uSec     9.79 MB/s
> quorumi: prun -N2 pgping -f get -b32 8
>   1:        8 bytes      0.79 uSec    10.18 MB/s


Or for those that distrust quoting pure powers of two in benchmarks and/or know too much bash:

[dan at quorumi]$ for ((i=1,j=1;$i<999;i=$i+$j,j=$i)) ;do echo -ne "pipelining \t$i:\t"; prun -N2 pgping -f get -b$i 64|cut -c20-35; done
pipelining      1:            2.39 uSec
pipelining      2:            1.38 uSec
pipelining      3:            1.24 uSec
pipelining      5:            1.05 uSec
pipelining      8:            0.92 uSec
pipelining      13:           0.91 uSec
pipelining      21:           0.86 uSec
pipelining      34:           0.80 uSec
pipelining      55:           0.78 uSec
pipelining      89:           0.79 uSec
pipelining      144:          0.77 uSec
pipelining      233:          0.73 uSec
pipelining      377:          0.77 uSec
pipelining      610:          0.78 uSec
pipelining      987:          0.77 uSec

Note that the above is for 64 *byte* reads which iirc is what Vincent was targetting.

Daniel.

--------------------------------------------------------------
Dr. Dan Kidger, Quadrics Ltd.      daniel.kidger at quadrics.com
One Bridewell St., Bristol, BS1 2AA, UK         0117 915 5505
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