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On 02/05/15 15:10, Volker Armin Hemmann wrote: |
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> Am 02.05.2015 um 14:06 schrieb Nikos Chantziaras: |
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>> On 02/05/15 14:37, Volker Armin Hemmann wrote: |
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>>> Am 02.05.2015 um 13:25 schrieb Nikos Chantziaras: |
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>>>>>> |
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>>>>>> The kernel uses -O2 and several -march variants (e.g. -march=core2). |
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>>>>>> Several other options are used to prevent GCC from generating |
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>>>>>> unsuitable code. |
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>>>>>> |
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>>>>>> Specifying another -march variant does not affect the optimizer |
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>>>>>> though. It only affects the code generator. If you don't modify the |
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>>>>>> other CFLAGS and only change -march, you will not get FP instructions |
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>>>>>> unless you use FP in the code. |
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>>>>> |
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>>>>> http://www.agner.org/optimize/calling_conventions.pdf |
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>>>> |
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>>>> Not sure what you're trying to say. |
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>>>> |
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>>> |
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>>> that simd is not save in kernel if not carefully guarded. |
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>>> |
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>>> Really people, just don't fuck around with the cflags. |
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>> |
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>> I still fail to see the relevance. Unless you mean using a different |
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>> -O level. In that case, yes. You shouldn't. But I was talking about |
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>> -march. |
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>> |
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> |
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> you said this |
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> |
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>> |
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>> (note that SIMD is not FP and is perfectly fine in the kernel.) |
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> |
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> and I have shown you that you are wrong. |
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|
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Not sure why you think that. The kernel crypto routines are full of SIMD |
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code (like SSE and AVX.) Automatic vectorization wouldn't work. But |
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-march is not going to introduce that. |
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