Re: [Buildroot] [PATCH v4 04/13] package/gemmlowp: new package

["Yann E. MORIN" <yann.morin.1998@free.fr>]

James, All,

On 2023-01-27 07:10 -0700, James Hilliard spake thusly:
> From: Stefan Hager <stefan.hager@ginzinger.com>
> 
> This package is required by tensorflow-lite.
> 
> Tested-by: Stefan Hager <stefan.hager@ginzinger.com>
> Signed-off-by: Stefan Hager <stefan.hager@ginzinger.com>
> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
> ---
[--SNIP--]
> diff --git a/package/gemmlowp/gemmlowp.mk b/package/gemmlowp/gemmlowp.mk
> new file mode 100644
> index 0000000000..1a36fc48f7
> --- /dev/null
> +++ b/package/gemmlowp/gemmlowp.mk
> @@ -0,0 +1,15 @@
> +################################################################################
> +#
> +# gemmlowp
> +#
> +################################################################################
> +
> +GEMMLOWP_VERSION = 08e4bb339e34017a0835269d4a37c4ea04d15a69
> +GEMMLOWP_SITE = $(call github,google,gemmlowp,$(GEMMLOWP_VERSION))
> +GEMMLOWP_LICENSE = Apache-2.0
> +GEMMLOWP_LICENSE_FILES = LICENSE
> +GEMMLOWP_INSTALL_STAGING = YES
> +GEMMLOWP_INSTALL_TARGET = NO
> +GEMMLOWP_SUBDIR = contrib

Upstream is very careful to point to some optimisations that are
required or performance will suffer.

Notably, should be enabled:
  - for x86: sse4.1
  - for ARM: NEON

For NEON, it seems this is automatically handled, though, based on
looking at some macros:

    internal/detect_platform.h
    85 #if (defined __ARM_NEON) || (defined __ARM_NEON__)
    86 #define GEMMLOWP_NEON
    87 #endif

For x86, we should probably have code like (what we have as
BR2_X86_CPU_HAS_SSE4 seems to be SSE4.1, but it is not clear whether
there is an actual delta between SSE4 and SSE4.1 [0], so let's be safe
and assume that BR2_X86_CPU_HAS_SSE4 is not enough):

    ifeq ($(BR2_X86_CPU_HAS_SSE42),y)
    GEMMLOWP_OPTIM += -msse4.1
    endif

However, that same header seems to also have some detection based on
macros... This needs to be cleared, maybe?

[0] https://en.wikipedia.org/wiki/SSE4

Regards,
Yann E. MORIN.

> +$(eval $(cmake-package))
> -- 
> 2.34.1
> 
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