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subtle side effect of commit a1c48bb160f836

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  subtle side effect of  commit a1c48bb160f836 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-06-18 09:00 +0200
    Re: subtle side effect of commit a1c48bb160f836 Geert Uytterhoeven <geert@linux-m68k.org> - 2015-06-18 09:20 +0200
      Re: subtle side effect of commit a1c48bb160f836 Geert Uytterhoeven <geert@linux-m68k.org> - 2015-06-18 09:40 +0200
        Re: subtle side effect of commit a1c48bb160f836 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-06-18 10:10 +0200
      Re: subtle side effect of commit a1c48bb160f836 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-06-18 09:40 +0200
      Re: subtle side effect of commit a1c48bb160f836 Michal Marek <mmarek@suse.cz> - 2015-06-18 10:20 +0200

#1167606 — subtle side effect of commit a1c48bb160f836

Hi Geert,

commit a1c48bb160f8368 "Makefile: Fix unrecognized cross-compiler command line
options" moved ARCH specific cc option handling before common -Os/O2 setup.

For ARC this had a subtle effect that we can no longer over-ride generic -O2 with
-O3, hence a performance regression observed going from 3.13 to 3.18 (the above
commit went into 3.16)

I want to understand how to properly fix this. Moving the include of arch makefile
will bring back the old issue. I can introduce another option to set default optim
level, but only arc/m32r care about it anyways.

Thx,
-Vineet
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#1167621 — Re: subtle side effect of commit a1c48bb160f836

Hi Vineet,

On Thu, Jun 18, 2015 at 8:47 AM, Vineet Gupta
<Vineet.Gupta1@synopsys.com> wrote:
> commit a1c48bb160f8368 "Makefile: Fix unrecognized cross-compiler command line
> options" moved ARCH specific cc option handling before common -Os/O2 setup.
>
> For ARC this had a subtle effect that we can no longer over-ride generic -O2 with
> -O3, hence a performance regression observed going from 3.13 to 3.18 (the above
> commit went into 3.16)
>
> I want to understand how to properly fix this. Moving the include of arch makefile
> will bring back the old issue. I can introduce another option to set default optim
> level, but only arc/m32r care about it anyways.

Can we include $(srctree)/arch/$(SRCARCH)/Makefile twice?

Or perhaps we can not apply the extra -O* if there's already a -O* option?

Alternatively, as we already have CONFIG_CC_OPTIMIZE_FOR_SIZE,
a(nother) Kconfig option may make sense.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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#1167630 — Re: subtle side effect of commit a1c48bb160f836

On Thu, Jun 18, 2015 at 9:33 AM, Vineet Gupta
<Vineet.Gupta1@synopsys.com> wrote:
> On Thursday 18 June 2015 12:40 PM, Geert Uytterhoeven wrote:
>> On Thu, Jun 18, 2015 at 8:47 AM, Vineet Gupta
>> <Vineet.Gupta1@synopsys.com> wrote:
>>> > commit a1c48bb160f8368 "Makefile: Fix unrecognized cross-compiler command line
>>> > options" moved ARCH specific cc option handling before common -Os/O2 setup.
>>> >
>>> > For ARC this had a subtle effect that we can no longer over-ride generic -O2 with
>>> > -O3, hence a performance regression observed going from 3.13 to 3.18 (the above
>>> > commit went into 3.16)
>>> >
>>> > I want to understand how to properly fix this. Moving the include of arch makefile
>>> > will bring back the old issue. I can introduce another option to set default optim
>>> > level, but only arc/m32r care about it anyways.
>> Can we include $(srctree)/arch/$(SRCARCH)/Makefile twice?
>
> Something like this would be ideal, but does that not bring back your warnings ?

I don't think so. The warnings were caused by using the host compiler instead
of the cross compiler while checking for the support of some compiler options.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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#1167659 — Re: subtle side effect of commit a1c48bb160f836

On Thursday 18 June 2015 01:07 PM, Geert Uytterhoeven wrote:
>>> >> Can we include $(srctree)/arch/$(SRCARCH)/Makefile twice?
>> >
>> > Something like this would be ideal, but does that not bring back your warnings ?
> I don't think so. The warnings were caused by using the host compiler instead
> of the cross compiler while checking for the support of some compiler options.

Tried that but build system spews tons of warning about over-riding commands...

----->8-------
arch/arc/Makefile:103: warning: overriding commands for target `uImage'
arch/arc/Makefile:103: warning: ignoring old commands for target `uImage'
arch/arc/Makefile:103: warning: overriding commands for target `uImage.bin'
arch/arc/Makefile:103: warning: ignoring old commands for target `uImage.bin'
...
...
----->8-------



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#1167634 — Re: subtle side effect of commit a1c48bb160f836

On Thursday 18 June 2015 12:40 PM, Geert Uytterhoeven wrote:
> On Thu, Jun 18, 2015 at 8:47 AM, Vineet Gupta
> <Vineet.Gupta1@synopsys.com> wrote:
>> > commit a1c48bb160f8368 "Makefile: Fix unrecognized cross-compiler command line
>> > options" moved ARCH specific cc option handling before common -Os/O2 setup.
>> >
>> > For ARC this had a subtle effect that we can no longer over-ride generic -O2 with
>> > -O3, hence a performance regression observed going from 3.13 to 3.18 (the above
>> > commit went into 3.16)
>> >
>> > I want to understand how to properly fix this. Moving the include of arch makefile
>> > will bring back the old issue. I can introduce another option to set default optim
>> > level, but only arc/m32r care about it anyways.
> Can we include $(srctree)/arch/$(SRCARCH)/Makefile twice?

Something like this would be ideal, but does that not bring back your warnings ?

> 
> Or perhaps we can not apply the extra -O* if there's already a -O* option?

Could be, but I'm not sure how to do that ?


> Alternatively, as we already have CONFIG_CC_OPTIMIZE_FOR_SIZE,
> a(nother) Kconfig option may make sense.

I can cook this one - but is it really worth doing when only 2 arches care.

Michal, do you have any opinion on how to solve this ?

-Vineet
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#1167680 — Re: subtle side effect of commit a1c48bb160f836

On Thu, Jun 18, 2015 at 09:10:30AM +0200, Geert Uytterhoeven wrote:
> Hi Vineet,
> 
> On Thu, Jun 18, 2015 at 8:47 AM, Vineet Gupta
> <Vineet.Gupta1@synopsys.com> wrote:
> > commit a1c48bb160f8368 "Makefile: Fix unrecognized cross-compiler command line
> > options" moved ARCH specific cc option handling before common -Os/O2 setup.
> >
> > For ARC this had a subtle effect that we can no longer over-ride generic -O2 with
> > -O3, hence a performance regression observed going from 3.13 to 3.18 (the above
> > commit went into 3.16)
> >
> > I want to understand how to properly fix this. Moving the include of arch makefile
> > will bring back the old issue. I can introduce another option to set default optim
> > level, but only arc/m32r care about it anyways.

m32r only sets -O for its assembler.


> Can we include $(srctree)/arch/$(SRCARCH)/Makefile twice?

Please don't, the gcc commandline is long enough already.


> Or perhaps we can not apply the extra -O* if there's already a -O* option?
> 
> Alternatively, as we already have CONFIG_CC_OPTIMIZE_FOR_SIZE,
> a(nother) Kconfig option may make sense.

We can also introduce some ARCH_CFLAGS that is appended near the end of
the list, and have arc/Makefile add its -O3 there. But I'd like to why
the -O3 needs to be there in first place. Obviously, the kernel works
with -O2, otherwise the regression would have been identified earlier.
So why can't users specify -O3 in KCFLAGS like on any other
architecture.

Michal
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