On Fri, May 18, 2012 at 7:06 PM, Mohammad Mirzadeh <span dir="ltr"><<a href="mailto:mirzadeh@gmail.com" target="_blank">mirzadeh@gmail.com</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">Hi guys,<div><br></div><div>I'm trying to generate scalability plots for my code and do profiling and fine tuning. In doing so I have noticed that some of the factors affecting my results are sort of subtle. For example, I figured, the other day, that using all of the cores on a single node is somewhat (50-60%) slower when compared to using only half of the cores which I suspect is due to memory bandwidth and/or other hardware-related issues. </div>
<div><br></div><div>So I thought to ask and see if there is any example in petsc that has been tested for scalability and has been documented? Basically I want to use this test example as a benchmark to compare my results with. My own test code is currently a linear Poisson solver on an adaptive quadtree grid and involves non-trivial geometry (well basically a circle for the boundary but still not a simple box).</div>
</div></blockquote><div><br></div><div>Unfortunately, I do not even know what that means. We can't guarantee a certain level of performance because it not</div><div>only depends on the hardware, but how you use it (as evident in your case). In a perfect world, we would have an abstract</div>
<div>model of the computation (available for MatMult) and your machine (not available anywhere) and we would automatically</div><div>work out the consequences and tell you what to expect. Instead today, we tell you to look at a few key indicators like the</div>
<div>MatMult event, to see what is going on. When MatMult stops scaling, you have run out of bandwidth.</div><div><br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr"><div>Thanks,</div><div>Mohammad</div></div>
</blockquote></div><br><br clear="all"><div><br></div>-- <br>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>
-- Norbert Wiener<br>