From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Arnd Bergmann <arnd@arndb.de>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Paul Mackerras <paulus@samba.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
kbuild test robot <lkp@intel.com>,
Nathan Chancellor <natechancellor@gmail.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH] powerpc: fix inline asm constraints for dcbz
Date: Fri, 9 Aug 2019 17:00:41 -0500 [thread overview]
Message-ID: <20190809220041.GO31406@gate.crashing.org> (raw)
In-Reply-To: <20190809220301.Horde.AR6y4Bx4WGIq58V9K0En9g4@messagerie.si.c-s.fr>
On Fri, Aug 09, 2019 at 10:03:01PM +0200, Christophe Leroy wrote:
> Arnd Bergmann <arnd@arndb.de> a écrit :
>
> >On Fri, Aug 9, 2019 at 8:21 PM 'Nick Desaulniers' via Clang Built
> >Linux <clang-built-linux@googlegroups.com> wrote:
> >
> >> static inline void dcbz(void *addr)
> >> {
> >>- __asm__ __volatile__ ("dcbz %y0" : : "Z"(*(u8 *)addr) : "memory");
> >>+ __asm__ __volatile__ ("dcbz %y0" : "=Z"(*(u8 *)addr) :: "memory");
> >> }
> >>
> >> static inline void dcbi(void *addr)
> >> {
> >>- __asm__ __volatile__ ("dcbi %y0" : : "Z"(*(u8 *)addr) : "memory");
> >>+ __asm__ __volatile__ ("dcbi %y0" : "=Z"(*(u8 *)addr) :: "memory");
> >> }
> >
> >I think the result of the discussion was that an output argument only
> >kind-of
> >makes sense for dcbz, but for the others it's really an input, and clang is
> >wrong in the way it handles the "Z" constraint by making a copy, which it
> >doesn't do for "m".
> >
> >I'm not sure whether it's correct to use "m" instead of "Z" here, which
> >would be a better workaround if that works. More importantly though,
> >clang really needs to be fixed to handle "Z" correctly.
>
> As the benefit is null, I think the best is probably to reverse my
> original commit until at least CLang is fixed, as initialy suggested
> by mpe
And what about the other uses of "Z"?
Also, if you use C routines (instead of assembler code) for the basic
"clear a block" and the like routines, as there have been patches for
recently, the benefit is not zero.
Segher
next prev parent reply other threads:[~2019-08-09 22:01 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-29 20:25 [PATCH] powerpc: workaround clang codegen bug in dcbz Nick Desaulniers
2019-07-29 20:32 ` Nathan Chancellor
2019-07-29 20:45 ` Nick Desaulniers
2019-07-29 20:47 ` Nathan Chancellor
2019-07-29 20:49 ` Nick Desaulniers
2019-07-29 21:52 ` Segher Boessenkool
2019-07-30 7:34 ` Arnd Bergmann
2019-07-30 11:17 ` Michael Ellerman
2019-08-09 18:21 ` [PATCH] powerpc: fix inline asm constraints for dcbz Nick Desaulniers
2019-08-09 18:28 ` Arnd Bergmann
2019-08-09 20:03 ` Christophe Leroy
2019-08-09 20:12 ` Arnd Bergmann
2019-08-09 22:03 ` Nick Desaulniers
2019-08-09 22:10 ` Segher Boessenkool
2019-08-09 22:00 ` Segher Boessenkool [this message]
2019-08-09 22:03 ` [PATCH v3] Revert "powerpc: slightly improve cache helpers" Nick Desaulniers
2019-08-10 9:09 ` Michael Ellerman
2019-08-09 21:55 ` [PATCH] powerpc: fix inline asm constraints for dcbz Segher Boessenkool
2019-08-09 20:36 ` Nathan Chancellor
2019-07-30 13:48 ` [PATCH] powerpc: workaround clang codegen bug in dcbz Segher Boessenkool
2019-07-30 14:30 ` Arnd Bergmann
2019-07-30 16:16 ` Segher Boessenkool
2019-07-30 17:07 ` Segher Boessenkool
2019-07-30 18:24 ` Arnd Bergmann
2019-07-30 18:24 ` Arnd Bergmann
2019-07-30 19:35 ` Segher Boessenkool
2019-07-30 5:31 ` Christophe Leroy
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