[petsc-users] petsc example with known scalability

[Mohammad Mirzadeh]

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.

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
>
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