<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content="text/html; charset=us-ascii" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 8.00.6001.18828"></HEAD>
<BODY>
<DIV dir=ltr align=left><SPAN class=761180600-03112009><FONT color=#0000ff
size=2 face=Arial>You can see the algorithms used for different messages sizes
in MPICH2 here: <A
href="https://svn.mcs.anl.gov/repos/mpi/mpich2/trunk/src/mpi/coll/allgatherv.c">https://svn.mcs.anl.gov/repos/mpi/mpich2/trunk/src/mpi/coll/allgatherv.c</A>,
but Cray could be using a modified version. What is the total message size being
gathered and how many processes are you running on?</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=761180600-03112009><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=761180600-03112009><FONT color=#0000ff
size=2 face=Arial>Rajeev</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=761180600-03112009></SPAN> </DIV><BR>
<BLOCKQUOTE
style="BORDER-LEFT: #0000ff 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"
dir=ltr>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><B>From:</B> mpich-discuss-bounces@mcs.anl.gov
[mailto:mpich-discuss-bounces@mcs.anl.gov] <B>On Behalf Of </B>Justin
Luitjens<BR><B>Sent:</B> Monday, November 02, 2009 5:59 PM<BR><B>To:</B>
mpich-discuss@mcs.anl.gov<BR><B>Subject:</B> [mpich-discuss] MPI_Allgatherv
complexity<BR></FONT><BR></DIV>
<DIV></DIV>Hi,<BR><BR>I'm wondering what is the parallel complexity of
MPI_Allgatherv. I would suspect in the worst case it would be something
like N log P but from the timings i'm collecting this doesn't seem to be the
case. I'm running tests on Kraken (<A
href="http://www.nics.tennessee.edu/computing-resources/kraken"
target=_blank>http://www.nics.tennessee.edu/computing-resources/kraken</A>
<DIV id=:1qc class="ii gt">) and it looks like it might be something like P
log P.<BR><BR>Thanks,</DIV></BLOCKQUOTE></BODY></HTML>