Re: Questions about checksum feature in 9.3

On Sun, Sep 15, 2013 at 8:13 AM, Kevin <kevo@gatorgraphics.com> wrote:
> My attempts to compile it vectorized on OS X seemed to have failed since I don't find a vector instruction in the .o
fileeven though the options -msse4.1 -funroll-loops -ftree-vectorize should be supported according to the man page for
Apple'sllvm-gcc. 

I'm not sure what version of LLVM Apple is using for llvm-gcc. I know
that clang+llvm 3.3 can successfully vectorize the checksum algorithm
when -O3 is used.

> So, has anyone compiled checksum vectorized on OS X? Are there any performance data that would indicate whether or
notI should worry with this in the first place? 

Even without vectorization the worst case performance hit is about
20%. This is for a workload that is fully bottlenecked on swapping
pages in between shared buffers and OS cache. In real world cases it's
hard to imagine it having any measurable effect. A single core can
checksum several gigabytes per second of I/O without vectorization,
and about 30GB/s with vectorization.

Regards,
Ants Aasma
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