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dramatically different emerge times for gcc
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devsk
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PostPosted: Sun Sep 30, 2012 6:33 pm    Post subject: dramatically different emerge times for gcc Reply with quote

I have an x86 system where I have installed crossdev and what I find is that the cross-x86_64-pc-linux-gnu/gcc builds in 2.5mins whereas sys-devel/gcc builds in 13mins. Both are built with same USE flags and same version (4.7.2). Same holds true for binutils and glibc as well.

Is there an obvious reason for this large difference?
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Ant P.
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PostPosted: Mon Oct 01, 2012 1:50 am    Post subject: Reply with quote

The cross-compilers can't do the three stage bootstrap normal GCC does, for obvious reasons.
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devsk
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PostPosted: Mon Oct 01, 2012 2:18 am    Post subject: Reply with quote

Ant P. wrote:
The cross-compilers can't do the three stage bootstrap normal GCC does, for obvious reasons.
And glibc?
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toralf
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PostPosted: Mon Oct 01, 2012 9:58 am    Post subject: Re: dramatically different emerge times for gcc Reply with quote

devsk wrote:
I have an x86 system
...
where sys-devel/gcc builds in 13mins
Using ccache ?
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devsk
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PostPosted: Mon Oct 01, 2012 2:29 pm    Post subject: Re: dramatically different emerge times for gcc Reply with quote

toralf wrote:
devsk wrote:
I have an x86 system
...
where sys-devel/gcc builds in 13mins
Using ccache ?
yes. why would ccache slow down the build of gcc (or glibc for that matter)?
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toralf
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PostPosted: Mon Oct 01, 2012 4:35 pm    Post subject: Re: dramatically different emerge times for gcc Reply with quote

devsk wrote:
why would ccache slow down the build of gcc (or glibc for that matter)?
From the compilation times you gave it seems that you have many fast CPUs - ccache needs access to the (much more slower) disks (at least at the first run with low RAM).

To compare times, you should emerge the same package with and without ccache and/or twice in a row (with enough RAM ccache would benefit of the disk caching of linux).
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devsk
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PostPosted: Mon Oct 01, 2012 4:57 pm    Post subject: Re: dramatically different emerge times for gcc Reply with quote

toralf wrote:
devsk wrote:
why would ccache slow down the build of gcc (or glibc for that matter)?
From the compilation times you gave it seems that you have many fast CPUs - ccache needs access to the (much more slower) disks (at least at the first run with low RAM).

To compare times, you should emerge the same package with and without ccache and/or twice in a row (with enough RAM ccache would benefit of the disk caching of linux).
Without ccache, gcc emerged in 15mins. So, 2mins worse than with ccache, which is expected because there is a stage where it uses the existing compiler to build parts and they can safely come from ccache.

So, the question still remains: why would cross-compiled glibc/binutils compile in half the time compared to native? I think I am ready to buy multiple stages of gcc as an explanation for gcc's increased build time but glibc/binutils? Something is fishy about this.
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