Re: [PATCH] asm-generic: Force inlining of get_order() to work around gcc10 poor decision

Le 19/10/2020 à 10:32, Segher Boessenkool a écrit :

On Mon, Oct 19, 2020 at 07:50:41AM +0200, Christophe Leroy wrote:

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Le 19/10/2020 à 06:55, Joel Stanley a écrit :

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In the old days, marking a function 'static inline' was forcing
GCC to inline, but since commit ac7c3e4ff401 ("compiler: enable
CONFIG_OPTIMIZE_INLINING forcibly") GCC may decide to not inline
a function.

It looks like GCC 10 is taking poor decisions on this.

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1952 bytes smaller with your patch applied. Did you raise this with
anyone from GCC?

Yes I did, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445

For the time being, it's at a standstill.

The kernel should just use __always_inline if that is what it *wants*;
that is true here most likely.  GCC could perhaps improve its heuristics
so that it no longer thinks these functions are often too big for
inlining (they *are* pretty big, but not after basic optimisations with
constant integer arguments).

Yes I guess __always_inline is to be added on functions like this defined in headers for exactly 
that, and that's the purpose of this patch.

However I find it odd that get_order() is outlined by GCC even in some object files that don't use 
it at all, for instance in fs/pipe.o

Christophe