Re: [PATCH -tip] compiler_types.h: Optimize __unqual_scalar_typeof compilation time

[Arnd Bergmann]

On Wed, May 27, 2020 at 2:35 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
> On Wed, May 27, 2020 at 2:31 PM Arnd Bergmann <arnd@xxxxxxxx> wrote:
> > On Wed, May 27, 2020 at 1:36 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
> > > On Wed, May 27, 2020 at 1:27 PM Arnd Bergmann <arnd@xxxxxxxx> wrote:
> > > > On Wed, May 27, 2020 at 12:33 PM Marco Elver <elver@xxxxxxxxxx> wrote:
> > > >
> > > > This gives us back 80% of the performance drop on clang, and 50%
> > > > of the drop I saw with gcc, compared to current mainline.
> > > >
> > > > Tested-by: Arnd Bergmann <arnd@xxxxxxxx>
> > > >
> > >
> > > Hi Arnd,
> > >
> > > with "mainline" you mean Linux-next aka Linux v5.8 - not v5.7?
> >
> > I meant v5.7.
> >
> > > I have not seen __unqual_scalar_typeof(x) in compiler_types.h in Linux v5.7.
> > >
> > > Is there a speedup benefit also for Linux v5.7?
> > > Which patches do I need?
> >
> > v5.7-rc is the baseline and is the fastest I currently see. On certain files,
> > I saw an intermittent 10x slowdown that was already fixed earlier, now
> > linux-next
> > is more like 2x slowdown for me and 1.2x with this patch on top, so we're
> > almost back to the speed of linux-5.7.
> >
>
> Which clang version did you use - and have you set KCSAN kconfigs -
> AFAICS this needs clang-11?

I'm currently using clang-11, but I see the same problem with older
versions, and both with and without KCSAN enabled. I think the issue
is mostly the deep nesting of macros that leads to code bloat.

        Arnd