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Date: Thu, 27 Sep 2012 08:01:07 +0200
From: magnum <>
Subject: Re: sha512crypt-opencl

On 27 Sep, 2012, at 0:06 , Claudio André <> wrote:

> Hi, thanks again.
> 2012/9/26 Gifts <>
> Benchmark with 20 minutes JtR and 10 minutes cudaHashcat
>  And it is interesting, that Intel OpenCl SDK can't vectorize this
> kernel. I hadn't look deeply into code yet, was this kernel optimized
> for GPU?
> I suppose magnum have something interesting to say about Intel SDK. Let's hear from him.
> I don't have any Intel hardware, so i can't say anything useful. Nevertheless, the kernel that runs on CPU is not optimized for GPUs. It gives acceptable results on AMD CPUs (i would say it was optimized for it).
> Maybe, there are tricks one can use to help the Intel compiler "do the job". Anyone have any clues about it?
> Claudio

I have seen Intel SDK auto-vectorize code that did not have any "hints" nor used vector types. That's impressing. I have also seen (judging from performance) Intel fail to vectorize code that is very simple and that do use vector types. That's a lot less impressing, even annoying. AMD APP seems to handle the latter case better. Note that this is regardless of hardware - you can use Intel SDK with AMD hardware or vice versa. I use to install both on any hardware that does not have a GPU.

Another caveat: I've seen indications that when Intel reports "kernel <xyz> was not vectorized" while building, it only means it was not auto-vectorized from scalar source. I mean, if the code does use vector data types it hopefully ended up as SIMD code despite that message. This is confusing, I'd rather have it silent.


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