[Mesa-dev] [android-x86-devel] [RFC 6/7] android: enable x86 asm and sse4 for x86 and x86_64

[Zhen Wu]

2016-05-01 17:46 GMT+08:00 Emil Velikov <emil.l.velikov at gmail.com>:

> On 30 April 2016 at 18:36, Zhen Wu <wuzhen at jidemail.com> wrote:
> > 2016-04-29 18:22 GMT+08:00 Emil Velikov <emil.l.velikov at gmail.com>:
> >>
> >> On 28 April 2016 at 08:34, Chih-Wei Huang <cwhuang at android-x86.org>
> wrote:
> >> > From: WuZhen <wuzhen at jidemail.com>
> >> >
> >> > Support multilib compilation use runtime feature selection.
> >> >
> >> > NO_REF_TASK
> >> > tested: local run
> >> >
> >> > Change-Id: Iee7961effdecde09cfbdaf09455bfb0912699ae3
> >> > Signed-off-by: Chih-Wei Huang <cwhuang at linux.org.tw>
> >> > ---
> >> >  Android.common.mk                    | 21 ++++++++++++++++++---
> >> >  Android.mk                           |  5 -----
> >> >  src/mapi/Android.mk                  |  3 +++
> >> >  src/mesa/Android.gen.mk              | 25 ++++++++++++++++++-------
> >> >  src/mesa/Android.libmesa_dricore.mk  | 20 +++++++++-----------
> >> >  src/mesa/Android.libmesa_sse41.mk    |  5 ++++-
> >> >  src/mesa/Android.libmesa_st_mesa.mk  | 20 +++++++++-----------
> >> >  src/mesa/Android.mesa_gen_matypes.mk |  7 +++++--
> >> >  src/mesa/drivers/dri/i965/Android.mk |  5 -----
> >> >  9 files changed, 66 insertions(+), 45 deletions(-)
> >> >
> >>
> >> Afact this patch does a few things:
> >>  - Moves -DUSE_SSE41 to the top level - good idea [patch 1]
> >>  - Consolidates -msse41 to libmesa_sse41.mk (effectively adding it to
> >> st_mesa) - good idea/bugfix.
> >> Take a look into configure.ac's add -mstackrealign (and the commit
> >> that introduced it). You might want the same/similar fix. [patch 2]
> >>
> >>  - Forces SSE4.1 even if there is no support for it. I.e.
> >> ARCH_X86_HAVE_SSE4_1 checks were dropped - very bad idea, please
> >> don't.
> >
> >
> > mesa seems always check for SSE4.1 support before using any of sse4.1
> > functions, if you are talking about compiler support for sse4.1, the
> > toolchain used in android should always support this. I only changed that
> > into always generate sse4.1 and rely on those runtion checks to avoid
> issues
> > on system without sse4.1 support, do you think this is a issue?
> >
> I'm thinking about a few things here:
>  - If someone is to have a hacked kernel which always advertises
> SSE4.1, even if it's not done natively but via emulation.
> Thus the actual usefulness of these codepaths will be... limited.
>  - The patch removes what seems to me a good approach only to replace
> it with a hacky version - the x86/x86-64 specific flags.
>

If someone were go to such length as to faking CPUID results, there is
really nothing we can do to stop them. The issue with
original flag is that it makes this feature test solely in build time, when
that flag is defined, it add -msse4.1 globally. but if undefined, we're
crippling users that do have SSE4.1 support. And I think this is the same
behavior as with autoconf builds, where USE_SSE41 is defined
if the compiler supports it.


> >>  - Adds separate (x86 and x86-64) SSE4.1 flags and libraries - not
> >> needed afaict, drop ?
> >
> >
> > I'm trying to avoid not breaking non-x86 builds.  this  is to seems
> better
> > than to surround them in a if clause. especially if we're to add flags
> for
> > other architectures.
> >
> The non-x86 build(s) end up broken because the ARCH_X86_HAVE_SSE4_1
> check was dropped. Please keep that one and then you won't need this
> workaround.


> >>  - Has some trailing '\' in which should cause build warning/errors -
> >> see comments below
> >>  - Gets "asm" building when host_arch != target_arch - have you guys
> >> tested it. what is the perf. improvement ? [patch 3]
> >
> >
> > No, we have not. We're trying to be in line to other platforms.
> >
> Although very admirable that you want to keep things in sync with the
> autoconf build, please don't add code that hasn't been tested.
> Note: this isn't that strict of a rule about the Android build
> although the asm code is very picky/fragile. I'm trying to avoid very
> nasty/subtle explosions.
>

Agreed


>
> Thanks
> Emil
>
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