linux-kernel - Re: [patch 14/15] lib/vdso: Avoid highres update if clocksource is not VDSO capable

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Date:   Wed, 15 Jan 2020 06:54:25 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, John Stultz <john.stultz@...aro.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paulburton@...nel.org>,
        James Hogan <jhogan@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>
Subject: Re: [patch 14/15] lib/vdso: Avoid highres update if clocksource is
 not VDSO capable



Le 14/01/2020 à 19:52, Thomas Gleixner a écrit :
> If the current clocksource is not VDSO capable there is no point in
> updating the high resolution parts of the VDSO data.
> 
> Replace the architecture specific check with a check for a VDSO capable
> clocksource and skip the update if there is none.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>   arch/arm/include/asm/vdso/vsyscall.h |    7 -------
>   include/asm-generic/vdso/vsyscall.h  |    7 -------
>   kernel/time/vsyscall.c               |   14 +++++++-------
>   3 files changed, 7 insertions(+), 21 deletions(-)
> 
> --- a/arch/arm/include/asm/vdso/vsyscall.h
> +++ b/arch/arm/include/asm/vdso/vsyscall.h
> @@ -22,13 +22,6 @@ struct vdso_data *__arm_get_k_vdso_data(
>   #define __arch_get_k_vdso_data __arm_get_k_vdso_data
>   
>   static __always_inline
> -bool __arm_update_vdso_data(void)
> -{
> -	return cntvct_ok;
> -}
> -#define __arch_update_vdso_data __arm_update_vdso_data
> -
> -static __always_inline
>   void __arm_sync_vdso_data(struct vdso_data *vdata)
>   {
>   	flush_dcache_page(virt_to_page(vdata));
> --- a/include/asm-generic/vdso/vsyscall.h
> +++ b/include/asm-generic/vdso/vsyscall.h
> @@ -11,13 +11,6 @@ static __always_inline struct vdso_data
>   }
>   #endif /* __arch_get_k_vdso_data */
>   
> -#ifndef __arch_update_vdso_data
> -static __always_inline bool __arch_update_vdso_data(void)
> -{
> -	return true;
> -}
> -#endif /* __arch_update_vdso_data */
> -
>   #ifndef __arch_update_vsyscall
>   static __always_inline void __arch_update_vsyscall(struct vdso_data *vdata,
>   						   struct timekeeper *tk)
> --- a/kernel/time/vsyscall.c
> +++ b/kernel/time/vsyscall.c
> @@ -71,15 +71,15 @@ void update_vsyscall(struct timekeeper *
>   {
>   	struct vdso_data *vdata = __arch_get_k_vdso_data();
>   	struct vdso_timestamp *vdso_ts;
> +	s32 clock_mode;
>   	u64 nsec;
> -	s32 mode;

Can we name is clock_mode in patch 9 instead of changing name here ?

Christophe

>   
>   	/* copy vsyscall data */
>   	vdso_write_begin(vdata);
>   
> -	mode = tk->tkr_mono.clock->vdso_clock_mode;
> -	vdata[CS_HRES_COARSE].clock_mode	= mode;
> -	vdata[CS_RAW].clock_mode		= mode;
> +	clock_mode = tk->tkr_mono.clock->vdso_clock_mode;
> +	vdata[CS_HRES_COARSE].clock_mode	= clock_mode;
> +	vdata[CS_RAW].clock_mode		= clock_mode;
>   
>   	/* CLOCK_REALTIME also required for time() */
>   	vdso_ts		= &vdata[CS_HRES_COARSE].basetime[CLOCK_REALTIME];
> @@ -105,10 +105,10 @@ void update_vsyscall(struct timekeeper *
>   	WRITE_ONCE(vdata[CS_HRES_COARSE].hrtimer_res, hrtimer_resolution);
>   
>   	/*
> -	 * Architectures can opt out of updating the high resolution part
> -	 * of the VDSO.
> +	 * If the current clocksource is not VDSO capable, then spare the
> +	 * update of the high reolution parts.
>   	 */
> -	if (__arch_update_vdso_data())
> +	if (clock_mode != VDSO_CLOCKMODE_NONE)
>   		update_vdso_data(vdata, tk);
>   
>   	__arch_update_vsyscall(vdata, tk);
>