Messages in this thread | | | Date | Tue, 20 Jun 2017 11:59:38 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] compiler, clang: Add always_inline attribute to inline |
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On Mon, Jun 19, 2017 at 03:19:27PM -0700, Sodagudi Prasad wrote: > On 2017-06-19 14:42, David Rientjes wrote: > >Yes, the arch/arm64/include/asm/cmpxchg.h instance appears to need > >__always_inline as several other functions need __always_inline in > >arch/arm64/include/*. It's worth making that change as you > >suggested in > >your original patch. > > > >The concern, however, is inlining all "inline" functions > >forcefully. The > >only reason this is done for gcc is because of suboptimal inlining > >decisions in gcc < 4. > > > >So the question is whether this is a single instance that can be fixed > >where clang un-inlining causes problems or whether that instance > >suggests > >all possible inline usage for clang absolutely requires __always_inline > >due to a suboptimal compiler implementation. I would suggest the > >former. > > Hi David, > > I am not 100% sure about the best approach for this problem. We may > have to > replace inline with always_inline for all inline functions where > BUILD_BUG() used. > > So far inline as always_inline for ARM64, if we do not continue same > settings, > will there not be any performance differences? > > Hi Will and Mark, > > Please suggest the best solution to this problem. Currently > __xchg_mb is only having issue > based on compiler -inline-threshold configuration. But there are > many other instances > in arch/arm64/* where BUILD_BUG() used for inline functions and > which may fail later.
As with my reply to David, my preference would be that we:
1) Align compiler-clang.h with the compiler-gcc.h inlining behaviour, so that things work by default.
2) Fix up the arm64 core code (and drivers for architected / common peripherals) to use __always_inline where we always require inlining.
3) Have arm64 select CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING, and have people test-build configurations with CONFIG_OPTIMIZE_INLINING, with both GCC and clang.
4) Fix up drivers, etc, as appropriate.
5) Once that's largely stable, and if there's a benefit, have arm64 select CONFIG_OPTIMIZE_INLINING by default.
That should avoid undue breakage, while enabling this ASAP.
Thanks, Mark.
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