Re: [PATCH RFC] x86: enforce inlining for atomics

[Ingo Molnar <mingo@kernel.org>]

* Markus Trippelsdorf <markus@trippelsdorf.de> wrote:

> On 2015.04.22 at 07:58 +0200, Hagen Paul Pfeifer wrote:
> > * Markus Trippelsdorf | 2015-04-22 07:24:41 [+0200]:
> > >I cannot reproduce this issue with my config with 4.8, 4.9 or 5. Could
> > >you please come up with a small testcase and open a gcc bug (with full
> > >gcc command line)?
> > 
> > the attached config file should do the trick. Can you try it?
> 
> It is definitely a -O2 vs. -Os issue. With your config:
> 
> -Os:
>  % nm vmlinux | grep " atomic_" | wc -l
> 736 
> 
> -O2 is fine:
>  % nm vmlinux | grep " atomic_"
> ffffffff852d8300 r atomic_counters_ops
> ffffffff83d66bf0 t atomic_counters_read
> ffffffff8119cd30 T atomic_dec_and_mutex_lock
> ffffffff81172e10 T atomic_notifier_call_chain
> ffffffff81172b90 T atomic_notifier_chain_register
> ffffffff81172d70 T atomic_notifier_chain_unregister
> ffffffff844b0ef0 t atomic_read_file
> ffffffff85a0c260 r atomic_ro_fops
> ffffffff87616000 d atomic_rw
> ffffffff852d8400 r atomic_stats_ops
> ffffffff83d66c50 t atomic_stats_read
> 
> The easiest fix would be to force always-inline in
> include/linux/compiler-gcc.h when CONFIG_CC_OPTIMIZE_FOR_SIZE is set.

That pretty much defeats the purpose of any inlining size calculations 
on -Os - and would make it impossible for better or bugfixed compilers 
to improve the situation.

So I think the original patch makes sense (and I already applied it), 
we want known-simple and performance critical methods (such as atomic 
ops) always inlined.

Thanks,

	Ingo