linux-kernel - Re: [PATCH v7 0/7] powerpc: switch VDSO to C implementation

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Date:   Mon, 20 Apr 2020 21:57:09 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v7 0/7] powerpc: switch VDSO to C implementation

On Mon, Apr 20, 2020 at 6:56 PM Christophe Leroy
<christophe.leroy@....fr> wrote:
>
> This is the seventh version of a series to switch powerpc VDSO to
> generic C implementation.
>
> Main changes since v6 are:
> - Added -fasynchronous-unwind-tables in CFLAGS
> - Split patch 2 in two parts
> - Split patch 5 (which was patch 4) in two parts
>
> This series applies on today's powerpc/merge branch.
>
> See the last two patches for details on changes and performance.
>
> Christophe Leroy (7):
>   powerpc/vdso64: Switch from __get_datapage() to get_datapage inline
>     macro
>   powerpc/vdso: Remove __kernel_datapage_offset and simplify
>     __get_datapage()
>   powerpc/vdso: Remove unused \tmp param in __get_datapage()
>   powerpc/processor: Move cpu_relax() into asm/vdso/processor.h
>   powerpc/vdso: Prepare for switching VDSO to generic C implementation.
>   powerpc/vdso: Switch VDSO to generic C implementation.

This all looks fine, but I'm a bit puzzled why you don't add a
clock_gettime64() implementation in the same series. Isn't
that the main purpose of doing all that work?

Without it, any 32-bit user space has to go through the system call
for time()/getttimeofday()/clock_gettime() when built with a
modern libc.

         Arnd