Re: [eigen] Eigen 3 is extremely slow

[Hari Sundar <hsundar@xxxxxxxxx>]

I am working on creating a simple example that I can share. I'll send you both the eigen and blitz versions. (if I am able to re-create the slowdown with the simple example)

thanks,
Hari

On Mon, Mar 14, 2011 at 9:57 AM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:

2011/3/14 Hari Sundar <hsundar@xxxxxxxxx>:

> I do not have any NaN values and I have checked it for my sample dataset.
>
> I did some additional tests and it appears that it is not the matrix
> multiplication itself that is slow, but it appears to be some really bad
> case of cache usage.
>
> Once projected, I use the points to sample from an Array (512x512). If I do
> not use Eigen for this array (instead using a std. C array), then my
> performance is much better.
>
> I hope that is able to point you in the right direction.

As Hauke said, the only useful thing would be a compilable test case.

Benoit

>
> I was using an ArrayXXf (also tried MatrixXf) to store the array.
>
> best,
> Hari
>
> On Mon, Mar 14, 2011 at 9:18 AM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
> wrote:
>>
>> 2011/3/14 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>:
>> > On Mon, Mar 14, 2011 at 12:48 AM, Hari Sundar <hsundar@xxxxxxxxx> wrote:
>> >> For example a simple 4x4 * 4*1 multiplication takes around 0.5msec.
>> >
>> > hm, that's indeed extremely slow... which compiler? flags?
>> >
>> > for instance here a 4x4 * 4x1 product takes less than 4e-6msec, and
>> > even in debug mode (-g2) with a very old gcc 3.4 it takes less than
>> > 0.0008 msec...
>>
>> If his matrix has NaN values, that could explain another 500x factor.
>>
>> Benoit
>>
>> >
>> > gael
>> >
>> >
>> >
>>
>>
>
>
>
> --
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> https://www.rad.upenn.edu/sbia/hsundar/
>

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