Am 02.05.2015 um 14:38 schrieb Nikos Chantziaras: > On 02/05/15 15:10, Volker Armin Hemmann wrote: >> Am 02.05.2015 um 14:06 schrieb Nikos Chantziaras: >>> On 02/05/15 14:37, Volker Armin Hemmann wrote: >>>> Am 02.05.2015 um 13:25 schrieb Nikos Chantziaras: >>>>>>> >>>>>>> The kernel uses -O2 and several -march variants (e.g. >>>>>>> -march=core2). >>>>>>> Several other options are used to prevent GCC from generating >>>>>>> unsuitable code. >>>>>>> >>>>>>> Specifying another -march variant does not affect the optimizer >>>>>>> though. It only affects the code generator. If you don't modify the >>>>>>> other CFLAGS and only change -march, you will not get FP >>>>>>> instructions >>>>>>> unless you use FP in the code. >>>>>> >>>>>> http://www.agner.org/optimize/calling_conventions.pdf >>>>> >>>>> Not sure what you're trying to say. >>>>> >>>> >>>> that simd is not save in kernel if not carefully guarded. >>>> >>>> Really people, just don't fuck around with the cflags. >>> >>> I still fail to see the relevance. Unless you mean using a different >>> -O level. In that case, yes. You shouldn't. But I was talking about >>> -march. >>> >> >> you said this >> >>> >>> (note that SIMD is not FP and is perfectly fine in the kernel.) >> >> and I have shown you that you are wrong. > > Not sure why you think that. The kernel crypto routines are full of > SIMD code (like SSE and AVX.) Automatic vectorization wouldn't work. > But -march is not going to introduce that
and never used in interrupt context and carefully guarded. You act like 'oh, you can use simd instructions without any consideration' and that is just not true.
