<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><br class=""></div> Because nemesis does function in a reasonable way when the system is oversubscribed, that is there are more MPI ranks than cores. Many users getting started have whatever number of cores (4?) but want to run tests with a few more ranks, this is not feasible with nemesis. In addition with the test harness we don't need to worry about the oversubscription issue and can run any number of ranks on any system.<div class=""><br class=""></div><div class=""> A possible alternative which means digging in the guts slightly is to default to nemesis BUT at PetscInitialize() if the user has selected more ranks than cores, stop and tell them they can't do that with nemesis and they must use sock if they want to do that. For the CI we would always use sock.</div><div class=""><br class=""></div><div class=""> Barry</div><div class=""><br class=""><div class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Jul 22, 2020, at 1:10 PM, Matthew Knepley <<a href="mailto:knepley@gmail.com" class="">knepley@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">We default to ch3:sock. Scott MacLachlan just had a long thread on the Firedrake list where it ended up that reconfiguring using ch3:nemesis had a 2x performance boost on his 16-core proc, and noticeable effect on the 4 core speedup.<div class=""><br class=""></div><div class="">Why do we default to sock?</div><div class=""><br class=""></div><div class=""> Thanks,</div><div class=""><br class=""></div><div class=""> Matt<br clear="all" class=""><div class=""><br class=""></div>-- <br class=""><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class="">What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br class="">-- Norbert Wiener</div><div class=""><br class=""></div><div class=""><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank" class="">https://www.cse.buffalo.edu/~knepley/</a><br class=""></div></div></div></div></div></div></div></div></div>
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