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Re: [PATCH 03/28] powerpc: Remove power4 mpa optimization
- From: "Gabriel F. T. Gomes" <gabriel at inconstante dot eti dot br>
- To: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- Cc: <libc-alpha at sourceware dot org>
- Date: Wed, 24 Apr 2019 18:51:44 -0300
- Subject: Re: [PATCH 03/28] powerpc: Remove power4 mpa optimization
- References: <email@example.com> <firstname.lastname@example.org>
On Fri, Mar 29 2019, Adhemerval Zanella wrote:
> This patch removes the POWER4 optimized mpa optimization used for power4+
> build. For newer chips, GCC generates *worse* code than generic
> implementation as benchmaks result below.
I don't think I have access to POWER4 hardware, but when running
power4-targeted builds on newer processors, I saw no performance
degradation even in that scenario.
> One possibilty would to add
> IFUNC variants for the mpa routines (as x86_64), but it will add complexity
> only for older chips (and one would need to check if power5, power5+, and
> power6 do benefict from this optimization), and only for specific
> implementation (since most used ones such as sin, cos, exp, pow already
> avoid calling the slow multiprecision path).
I don't think it's worth the effort.
> Checked on powerpc-linux-gnu (built without --with-cpu, with
> --with-cpu=power4 and with --with-cpu=power5+ and --disable-multi-arch),
> powerpc64-linux-gnu (built without --with-cp and with --with-cpu=power5+
> and --disable-multi-arch).
Thanks for the thorough checking.
> * sysdeps/powerpc/power4/fpu/Makefile: Remove file.
> * sysdeps/powerpc/power4/fpu/mpa-arch.h: Likewise.
> * sysdeps/powerpc/power4/fpu/mpa.c: Likewise.
Looks good to me.
Reviewed-by: Gabriel F. T. Gomes <email@example.com>