linux-kernel - Re: [PATCH -tip] compiler_types.h: Optimize __unqual_scalar

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Date:   Wed, 27 May 2020 14:31:06 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Marco Elver <elver@...gle.com>, Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH -tip] compiler_types.h: Optimize __unqual_scalar_typeof
 compilation time

On Wed, May 27, 2020 at 1:36 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
> On Wed, May 27, 2020 at 1:27 PM Arnd Bergmann <arnd@...db.de> wrote:
> > On Wed, May 27, 2020 at 12:33 PM Marco Elver <elver@...gle.com> 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@...db.de>
> >
>
> 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.

      Arnd