[SimGrid-user] Latency issues

Tristan Glatard tglatard at encs.concordia.ca
Wed Jul 5 03:52:39 CEST 2017


We're trying to simulate a latency-bound application with Simgrid 3.16 
using MSG, and we're a bit puzzled by simulation times.

In example "app-pingpong" the ping time between hosts Tremblay and 
Jupiter, i.e., the time for Jupiter to receive a 1-bit task from 
Tremblay, is 0.019014s while the latency of the link between Tremblay 
and Jupiter (id 9 in small_platform.xml) is only 1.461517ms (factor 13 
difference). And if we edit the platform to contain only the bare 
minimal (2 hosts and 1 link with 1ms latency, see attached), we still 
get a ping time of 13ms while we would expect 1ms:

> [glatard at sapajou app-pingpong]$ ./app-pingpong ./smaller_platform.xml 
> ./app-pingpong_d.xml
> [Tremblay:pinger:(1) 0.000000] [mag_app_pingpong/INFO] Ping -> Jupiter
> [Jupiter:ponger:(2) 0.000000] [mag_app_pingpong/INFO] Pong -> Tremblay
> [Jupiter:ponger:(2) 0.013010] [mag_app_pingpong/INFO] Task received : 
> small communication (latency bound)
> [Jupiter:ponger:(2) 0.013010] [mag_app_pingpong/INFO]  Ping time 
> (latency bound) 0.013010
> [Jupiter:ponger:(2) 0.013010] [mag_app_pingpong/INFO] task_bw->data = 
> 0.013
> [Tremblay:pinger:(1) 150.166348] [mag_app_pingpong/INFO] Task received 
> : large communication (bandwidth bound)
> [Tremblay:pinger:(1) 150.166348] [mag_app_pingpong/INFO] Pong time 
> (bandwidth bound): 150.153
> [150.166348] [mag_app_pingpong/INFO] Total simulation time: 150.166
The same factor-13 difference is still observed on a different but 
similar application.

Do you have any idea what's going on?



Tristan Glatard

Assistant Professor, Dept of Computer Science and Software Engineering, 
Concordia University

Office: EV 6.225

Phone: +1 514 848 2424, ext 5888
Cell: +1 514 660 9179

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smaller_platform.xml
Type: text/xml
Size: 410 bytes
Desc: not available
URL: <http://lists.gforge.inria.fr/pipermail/simgrid-user/attachments/20170704/1dc7837f/attachment.xml>

More information about the Simgrid-user mailing list