On 2021-06-18 21:45, John Peterson wrote:
On Thu, Jun 10, 2021 at 5:55 PM edgar <edgar...@cryptolab.net> wrote:
On 2021-06-10 19:27, John Peterson wrote:
> I recorded the "Active time" for the "Matrix Assembly Performance"
> PerfLog
> in introduction_ex4 running "./example-opt -d 3 -n 40" for both the
> original codepath and your proposed change, averaging the results over
> 5
> runs. The results were:
>
> Original code, "./example-opt -d 3 -n 40"
> import numpy as np
> np.mean([3.91801, 3.93206, 3.94358, 3.97729, 3.90512]) = 3.93
>
> Patch, "./example-opt -d 3 -n 40"
> import numpy as np
> np.mean([4.10462, 4.06232, 3.95176, 3.92786, 3.97992]) = 4.00
>
> so I'd say the original code path is marginally (but still
> statistically
> significantly) faster, although keep in mind that matrix assembly is
> only
> about 21% of the total time for this example while the solve is about
> 71%.
Superinteresting, I am sending you my benchmarks. I must say that I
had
initially run only 2 benchmarks, and both came out faster with the
modifications. Now, I found that
- The original code is more efficient with `-n 40'
- The modified code is more efficient with `-n 15' and `mpirun -np 4'
- That I ran the 5-test trial several times and some times, the
original
code was more efficient with `-n 15', but the first and second run
with
the modified code were always faster (my computer heating up?)
The gains are really marginal in any case. It would be interesting to
run with -O3... (I just did [1]).
It seems that the differences are now a little bit more substantial,
and
that the modified code would be faster. I hope not to have made any
mistakes.
The code and the benchmarks are in the attached file.
- examples
|- introduction
|- ex4 (original code)
|- output_*_.txt.bz2 (running -n 40 with -O2)
|- output_15_*_.txt.bz2 (running -n 15 with -O2)
|- output_40_O3_*_.txt.bz2 (running -n 40 with -O3)
|- ex4_mod (modified code)
|- output_*_.txt.bz2 (running -n 40 with -O2)
|- output_15_*_.txt.bz2 (running -n 15 with -O2)
|- output_40_O3_*_.txt.bz2 (running -n 40 with -O3)
[1] I manually compiled like this (added -O3 instead of -O2; disregard
the CCFLAGS et al):
$ mpicxx -std=gnu++17 -DNDEBUG -march=amdfam10 -O3
Your compiler flags are definitely far more advanced/aggressive than
mine,
which are just on the default of -O2. However, I think what we should
conclude from your results is that there is something slower than it
needs
to be with DenseMatrix::resize(), not that we should move the
DenseMatrix
creation/destruction inside the loop over elements. What I tried (see
attached patch or the "dense_matrix_resize_no_virtual" branch in my
fork)
is avoiding the virtual function call to DenseMatrix::zero() which is
currently made from DenseMatrix::resize(). In my testing, this change
did
not seem to make much of a difference but I'm curious about what you
would
get with your compiler args, this patch, and the unpatched ex4.
I will surely test it. I will have more time next week. Sorry for the
delay.
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