I noticed this morning that the loop are in the wrong order for a column
major array. Reversing them, I get:
testing outer_func
0.294904 seconds
0.296689 seconds
testing outer_func2
0.280391 seconds
0.281223 seconds
Now both versions have the phi instructions, so I guess that wasn't the
problem
And sprinkling a little @simd on the inner loops:
testing outer_func
0.159910 seconds
0.157640 seconds
testing outer_func2
0.151384 seconds
0.152224 seconds
I'm going to write a Fortran code to do a performance comparison, but this
is looking pretty good.
Do you think I should file a performance issue for the original code?
Jared Crean
On Saturday, October 29, 2016 at 4:13:48 AM UTC-4, Kristoffer Carlsson
wrote:
>
> Could it be some alias checking going on?
>
> Anyway, this code is horribly slow on 0.6 (even with #19097) it seems.
>
> to_indexes(::Int64, ::Int64, ::Vararg{Int64,N}) at operators.jl:868
> (repeats 3 times)
> kills performance.
>
>
> On Saturday, October 29, 2016 at 5:56:12 AM UTC+2, Jared Crean wrote:
>>
>> I'm working on an high dimensional finite difference code, and I got a
>> strange performance result. I have a kernel function that
>> computes the stencil at a given point, and an outer function, outer_func,
>> that loops over the dimensions and calls the kernel function at every grid
>> point.
>> I created a second function, outer_func2, with the same loops as
>> outer_func, but rather than call the kernel function it has the contents of
>> the kernel function copied into it. The source code is here:
>> https://github.com/JaredCrean2/wave6d/blob/master/src/test_inline.jl
>>
>> The performance results (with bounds checking disabled and
>> --math-mode=fast) are:
>>
>> testing outer_func
>> 0.398586 seconds
>> 0.398821 seconds
>> testing outer_func2
>> 2.522230 seconds
>> 2.522479 seconds
>>
>>
>>
>> I ran this on in Intel Ivy Bridge (i7-3820) processor, using Julia 0.4.4
>>
>> I looked at the llvm code (attached), and noticed outer_func2 has a bunch
>> of extra statements that look like
>>
>> %lsr.iv570 = phi i8* [ %scevgep571, %L21 ], [ %scevgep569, %L.preheader
>> ]
>>
>>
>>
>> that are not present for outer_func. I don't know llvm code very well
>> (hardly at all), so I'm not sure what these mean. Any help
>> understanding either the llvm code or the performance difference would be
>> appreciated.
>>
>>
>>
>> Thanks,
>> Jared Crean
>>
>
