Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Clarifiy performance results #18242

Merged
merged 1 commit into from
Aug 26, 2016
Merged

Clarifiy performance results #18242

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
15 changes: 7 additions & 8 deletions doc/manual/performance-tips.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1068,20 +1068,21 @@ Here is an example with both :obj:`@inbounds` and :obj:`@simd` markup::
time = @elapsed for j in 1:reps
s+=inner(x,y)
end
println("GFlop = ",2.0*n*reps/time*1E-9)
println("GFlop/sec = ",2.0*n*reps/time*1E-9)
time = @elapsed for j in 1:reps
s+=innersimd(x,y)
end
println("GFlop (SIMD) = ",2.0*n*reps/time*1E-9)
println("GFlop/sec (SIMD) = ",2.0*n*reps/time*1E-9)
end

timeit(1000,1000)

On a computer with a 2.4GHz Intel Core i5 processor, this produces::

GFlop = 1.9467069505224963
GFlop (SIMD) = 17.578554163920018
GFlop/sec = 1.9467069505224963
GFlop/sec (SIMD) = 17.578554163920018

(``GFlop/sec`` measures the performance, and larger numbers are better.)
The range for a ``@simd for`` loop should be a one-dimensional range.
A variable used for accumulating, such as ``s`` in the example, is called
a *reduction variable*. By using :obj:`@simd`, you are asserting several
Expand Down Expand Up @@ -1167,13 +1168,11 @@ evaluates the L2-norm of the result::

On a computer with a 2.7 GHz Intel Core i7 processor, this produces::

$ julia wave.jl
$ julia wave.jl;
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

FWIW the output comes from the println and not the command line.....

elapsed time: 1.207814709 seconds (0 bytes allocated)
4.443986180758243

$ julia --math-mode=ieee wave.jl
$ julia --math-mode=ieee wave.jl;
elapsed time: 4.487083643 seconds (0 bytes allocated)
4.443986180758243

Here, the option ``--math-mode=ieee`` disables the :obj:`@fastmath`
macro, so that we can compare results.
Expand Down