_performance_build and -O3 package builds

[Florian Weimer]

Downstream, we had a separate set of builds flags for certain packages
and used -O3 there, targeted at POWER (both ppc64 and ppc64le), for
increased use of vectorization presumably.

I don't think this was ever upstreamed to Fedora (the downstream changes
were in the redhat-rpm-config package).  I don't recall seeing a
corresponding Fedora change.  As a result, the recent downstream rebase
lost support for this.

Should Fedora package maintainers remove _performance_build support or
custom flag overrides for -O3 from their packages?

My understanding is that Fedora build flag policy is set by the
redhat-rpm-config package, which currently specifies -O2 for all
architectures.

Thanks,
Florian

[Kevin Fenzi]

On 12/10/18 3:56 AM, Florian Weimer wrote:
>  Downstream, we had a separate set of builds flags for certain
> packages
>  and used -O3 there, targeted at POWER (both ppc64 and ppc64le), for
>  increased use of vectorization presumably.
>  
>  I don't think this was ever upstreamed to Fedora (the downstream changes
>  were in the redhat-rpm-config package).  I don't recall seeing a
>  corresponding Fedora change.  As a result, the recent downstream rebase
>  lost support for this.
>  
>  Should Fedora package maintainers remove _performance_build support or
>  custom flag overrides for -O3 from their packages?
>  
>  My understanding is that Fedora build flag policy is set by the
>  redhat-rpm-config package, which currently specifies -O2 for all
>  architectures. 
Well, we have:
https://fedoraproject.org/wiki/Packaging:Guidelines#Compiler_flags

So, I would say anyone using those custom flags/overrides needs to
document why in spec and in general shouldn't override or use custom
flags. ;)

kevin

[Igor Gnatenko]

I think providing some simple way how to turn -O3 (or even some other
flags) would be interesting idea.

So I would love to see ticket for FPC and corresponding patch for
redhat-rpm-config.
On Mon, Dec 10, 2018 at 1:05 PM Florian Weimer <fweimer(a)redhat.com&gt; wrote:
>
> Downstream, we had a separate set of builds flags for certain packages
> and used -O3 there, targeted at POWER (both ppc64 and ppc64le), for
> increased use of vectorization presumably.
>
> I don't think this was ever upstreamed to Fedora (the downstream changes
> were in the redhat-rpm-config package).  I don't recall seeing a
> corresponding Fedora change.  As a result, the recent downstream rebase
> lost support for this.
>
> Should Fedora package maintainers remove _performance_build support or
> custom flag overrides for -O3 from their packages?
>
> My understanding is that Fedora build flag policy is set by the
> redhat-rpm-config package, which currently specifies -O2 for all
> architectures.
>
> Thanks,
> Florian
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[Peter Robinson]

>  Downstream, we had a separate set of builds flags for certain
> packages
>  and used -O3 there, targeted at POWER (both ppc64 and ppc64le), for
>  increased use of vectorization presumably.
>
>  I don't think this was ever upstreamed to Fedora (the downstream changes
>  were in the redhat-rpm-config package).  I don't recall seeing a
>  corresponding Fedora change.  As a result, the recent downstream rebase
>  lost support for this. 
Not sure what you mean by upstreamed the downstream change, this was
in Fedora but around Fedora 26 the ppc64p7 sub architectured was
EOLed. Over all it was a yum hack and it wasn't supported in dnf and
we worked with IBM to move most of their optimisations to IFUNC or run
time detectable fast paths in the areas they felt needed specific
optimisations.

>  Should Fedora package maintainers remove _performance_build support
> or
>  custom flag overrides for -O3 from their packages? 
The supported sub-set of packages for this particular project were:
binutils bzip2 cyrus-sasl glibc httpd kernel libxml2 mariadb openssl
pam pcre php postfix postgresql python python3 sendmail xz zlib

And yes, any perf build bits in those pacakages, and probably some
dependencies, is unused and can be removed.

> My understanding is that Fedora build flag policy is set by the
> redhat-rpm-config package, which currently specifies -O2 for all
> architectures.
>
> Thanks,
> Florian
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