On 10/22/2010 02:05 PM, dan clark wrote: > Hi Gentle Readers! > > Is round trip latency expected to degrade linearly as more receivers are > added to a system given an equivalent number of messages sent? >
Yes, latency from origination to delivery for totem is 1/2 token rotation time on average. Token rotation time is mainly dependent on number of nodes and partially dependent on the time needed to use the udp services of the kernel to send messages in a token rotation. These can be generalized into a time of latency = 1/2 * node count * token processing time per node + time to send all messages during one rotation. Not exact, but pretty close if calculating for RT deadline purposes. Regards -steve > The attached test application attempts to capture the situation. The > basic setup is to start N receivers on 1-N different nodes, then run a > single sender which tracks the results in a log file on the system > distributing delays across multiple buckets. Note when changing the > number of receivers to result in a similar number of messages it is > necessary to modify the message count of the sender. > > For example: > Starting receivers with a simple script: > #!/bin/sh > cnt=1 > maxcnt=16 > host=`hostname -s` > echo $host > while (($cnt <= $maxcnt)) > do > corestart -s -c 1 -i 1 -j 2 -p 30000000 > ((cnt++)) > done > > And then start a single sender: > corestart -c 100 -i 1 -j 2 -p 1000000 > > By varying the number of receivers (and the associated message count) > the round trip latency degrades with the number of receivers in a > non-linear relationship. > > How are your results for 1-8 node systems? > > Any insights as to what may cause this anomaly, including a poorly > written test application :)! > thanks, > dan > ps. there are several other parameters that allow this test application > to exercise some interesting aspects of the library., such as running > the number if iterations up (-i) to test initialize/finalize logic. > > > > _______________________________________________ > Openais mailing list > [email protected] > https://lists.linux-foundation.org/mailman/listinfo/openais _______________________________________________ Openais mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/openais
