Yes, I'm looking at weak scalability right now. I'm using BiCGSTAB with BoomerAMG (all default options except for rtol = 1e-12). I've not looked into MF/s yet but I'll surely do to see if I'm having any problem there. So far, just timing the KSPSolve, I get [0.231, 0.238, 0.296, 0.451, 0.599] seconds/KSP iteration for p=[1, 4, 16, 64, 256] with almost 93K nodes (matrix-row) per proc. Which is not bad I guess but still increased by a factor of 3 for 256 proc. Problem is, I don't know how good/bad this is. In fact I'm not even sure that is a valid question to ask since it may be very problem dependent.
Something I just though about, how crucial is the matrix structure for KSP solvers? The nodes have bad numbering and I do partitioning to get a better one here. On Fri, May 18, 2012 at 4:47 PM, Matthew Knepley <knepley at gmail.com> wrote: > On Fri, May 18, 2012 at 7:43 PM, Mohammad Mirzadeh <mirzadeh at > gmail.com>wrote: > >> I see; well that's a fair point. So i have my timing results obtained via >> -log_summary; what should I be looking into for MatMult? Should I be >> looking at wall timings? Or do I need to look into MFlops/s? I'm sorry but >> I'm not sure what measure I should be looking into to determine scalability. >> > > Time is only meaningful in isolation if I know how big your matrix is, but > you obviously take the ratio to look how it is scaling. I am > assuming you are looking at weak scalability so it should remain constant. > MF/s will let you know how the routine is performing > independent of size, and thus is an easy way to see what is happening. It > should scale like P, and when that drops off you have > insufficient bandwidth. VecMDot is a good way to look at the latency of > reductions (assuming you use GMRES). There is indeed no > good guide to this. Barry should write one. > > Matt > > >> Also, is there any general meaningful advice one could give? in terms of >> using the resources, compiler flags (beyond -O3), etc? >> >> Thanks, >> Mohammad >> >> On Fri, May 18, 2012 at 4:18 PM, Matthew Knepley <knepley at gmail.com>wrote: >> >>> On Fri, May 18, 2012 at 7:06 PM, Mohammad Mirzadeh <mirzadeh at >>> gmail.com>wrote: >>> >>>> Hi guys, >>>> >>>> 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. >>>> >>>> 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). >>>> >>> >>> Unfortunately, I do not even know what that means. We can't guarantee a >>> certain level of performance because it not >>> only depends on the hardware, but how you use it (as evident in your >>> case). In a perfect world, we would have an abstract >>> model of the computation (available for MatMult) and your machine (not >>> available anywhere) and we would automatically >>> work out the consequences and tell you what to expect. Instead today, we >>> tell you to look at a few key indicators like the >>> MatMult event, to see what is going on. When MatMult stops scaling, you >>> have run out of bandwidth. >>> >>> Matt >>> >>> >>>> Thanks, >>>> Mohammad >>>> >>> >>> >>> >>> -- >>> What most experimenters take for granted before they begin their >>> experiments is infinitely more interesting than any results to which their >>> experiments lead. >>> -- Norbert Wiener >>> >> >> > > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120518/228cab52/attachment.htm>
