[Spread-users] Multicast and Performance issues

David Turland david.turland at shazamteam.com
Fri Mar 15 16:03:32 EST 2002

Currently using Spread in earnest and trying to reach the plateau of 1MB/sec 
multicast to 36  nodes(Athlon 1.2G,Fast ethernet, switched, local subnet). 
(This is the performance I was getting using LAM/MPI and a tree-based 
broadcast -  If I can't achieve this then I will tolerate the hit of 
incorporating failover support using LAM/MPI)

so far topping out at 333kB/sec; whether I choose RELIABLE or UNRELIABLE.

I feel Iam not configuring Mlticast correctly as this value is the same 
whether I use a unicast rather than Multicast address in spread.conf

Spread_Segment {


Spread_Segment {

I really know nothing about multicast and feel there is something more I need 
to be doing than choosing 'arbitrary' multicast addresses in the spread.conf

incidentally,there is an entry in the /etc/rc.local file pertaining to 

# Setup the default multicast route
/sbin/route add -net netmask dev eth0

I think I need some more info before I spproach our sys admin guys...

Currently the benchmark I am running uisngs two threads, one for  sending and 
receiving with synchronisation (cv) between the sending and receiving threads 
so that the acks from (one or all ; makes little differnece) of the receivers 
are received before the next sending iteration takes place. If I omit this 
lock step then the session is closed arbitrarily, I presume because excessive 
mesages are stacked up in a buffer.

Interestingly, I played with max packet size, up to 1MB, but with my current, 
(non-multicast?) configuration I saw no performance changes.

I love the concept of spread, there are bits of it I am taking for granted 
which will take an age in LAM/MPI or RMT or RMTP to implement but I need to 
reach the magic 1MB/sec, or beyond

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