Re: [Qemu-devel] [v2 1/2] cutils: add avx2 instruction optimization

[Juan Quintela <quintela@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> wrote:

>
> The main issue here is that you are not testing whether the compiler 
> supports gnu_indirect_function.
>
> I suggest that you start by moving the functions to util/buffer-zero.c
>
> Then the structure should be something like
>
> #ifdef CONFIG_HAVE_AVX2
> #include <immintrin.h>
> #endif
>
> ... define buffer_find_nonzero_offset_inner ...
> ... define can_use_buffer_find_nonzero_offset_inner ...
>
> #if defined CONFIG_HAVE_GNU_IFUNC && defined CONFIG_HAVE_AVX2
> ... define buffer_find_nonzero_offset_avx2 ...
> ... define can_use_buffer_find_nonzero_offset_avx2 ...
> ... define the indirect functions ...
> #else
> ... define buffer_find_nonzero_offset that just calls
> buffer_find_nonzero_offset_inner ...
> ... define can_use_buffer_find_nonzero_offset that just calls
> can_use_buffer_find_nonzero_offset_inner ...
> #endif

My understanding for this was that glibc is better than hand made asm,
and paolo4_memzero (or whatever was it called) was the best approach.
And just remove SSE.  Have I missed something?


Later, Juan.