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From: Andy Lutomirski <luto@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>,
	Andrew Lutomirski <luto@kernel.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Arnd Bergmann <arnd@arndb.de>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	X86 ML <x86@kernel.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	"open list:MIPS" <linux-mips@vger.kernel.org>
Subject: Re: [RFC PATCH v3 08/12] lib: vdso: allow arches to provide vdso data pointer
Date: Thu, 16 Jan 2020 12:22:41 -0800
Message-ID: <CALCETrWOENu2k3aGNO-oiY1Sj8=cG9mMZ8eOepHOzdu25vFVVA@mail.gmail.com> (raw)
In-Reply-To: <87k15rwuxm.fsf@nanos.tec.linutronix.de>

On Thu, Jan 16, 2020 at 2:35 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> static __maybe_unused int
> __cvdso_data_clock_gettime(clockid_t clock, struct __kernel_timespec *ts,
>                            const struct vdso_data *vd)
> {
>         .....
> }
>
> static __maybe_unused int
> __cvdso_clock_gettime(clockid_t clock, struct __kernel_timespec *ts)
> {
>         const struct vdso_data *vd = __arch_get_vdso_data();
>
>         return __cvdso_data_clock_gettime(clock, ts, vd);
> }
>
> and then use __cvdso_data_clock_gettime on PPC and let the other archs
> unmodified.
>
>

FWIW, I did some experiments on x86 with gcc 9.2.  gcc 9.2 uses
rip-relative accesses if I simplify the config enough and otherwise
materializes the pointer.  Presumably it decides that the code size
reduction is worth it if there are a lot of accesses.

I suspect that tglx's suggestion will be fine or at worst will add
negligible overhead on x86_64.

  reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-13 17:08 [RFC PATCH v3 00/12] powerpc: switch VDSO to C implementation Christophe Leroy
2020-01-13 17:08 ` [RFC PATCH v3 01/12] powerpc/64: Don't provide time functions in compat VDSO32 Christophe Leroy
2020-01-13 17:08 ` [RFC PATCH v3 02/12] powerpc/vdso: Switch VDSO to generic C implementation Christophe Leroy
2020-01-13 17:08 ` [RFC PATCH v3 03/12] lib: vdso: mark __cvdso_clock_getres() as static Christophe Leroy
2020-01-13 17:08 ` [RFC PATCH v3 04/12] lib: vdso: inline do_hres() and do_coarse() Christophe Leroy
2020-01-13 17:08 ` [RFC PATCH v3 05/12] lib: vdso: Avoid duplication in __cvdso_clock_getres() Christophe Leroy
2020-01-13 17:08 ` [RFC PATCH v3 06/12] lib: vdso: __iter_div_u64_rem() is suboptimal for 32 bit time Christophe Leroy
2020-01-14 11:31   ` Thomas Gleixner
2020-01-13 17:08 ` [RFC PATCH v3 07/12] powerpc/vdso: simplify __get_datapage() Christophe Leroy
2020-01-13 17:08 ` [RFC PATCH v3 08/12] lib: vdso: allow arches to provide vdso data pointer Christophe Leroy
2020-01-14 23:06   ` Thomas Gleixner
2020-01-15  6:15     ` Christophe Leroy
2020-01-16  9:16       ` Christophe Leroy
2020-01-16 10:35         ` Thomas Gleixner
2020-01-16 20:22           ` Andy Lutomirski [this message]
2020-01-13 17:08 ` [RFC PATCH v3 09/12] powerpc/vdso: provide inline alternative to __get_datapage() Christophe Leroy
2020-01-13 17:08 ` [RFC PATCH v3 10/12] powerpc/vdso: provide vdso data pointer from the ASM caller Christophe Leroy
2020-01-13 17:08 ` [RFC PATCH v3 11/12] lib: vdso: split clock verification out of __arch_get_hw_counter() Christophe Leroy
2020-01-13 17:08 ` [RFC PATCH v3 12/12] powerpc/vdso: provide __arch_is_hw_counter_valid() Christophe Leroy

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