linux-kernel - Re: [PATCH 08/10] clocksource/drivers/hyper-v: Handle sched

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Date:   Mon, 22 Feb 2021 23:17:51 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     sthemmin@...rosoft.com, kys@...rosoft.com, wei.liu@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        daniel.lezcano@...aro.org, arnd@...db.de,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 08/10] clocksource/drivers/hyper-v: Handle sched_clock
 differences inline

On Wed, Jan 27, 2021 at 12:23:43PM -0800, Michael Kelley wrote:
> While the Hyper-V Reference TSC code is architecture neutral, the
> pv_ops.time.sched_clock() function is implemented for x86/x64, but not
> for ARM64. Current code calls a utility function under arch/x86 (and
> coming, under arch/arm64) to handle the difference.
> 
> Change this approach to handle the difference inline based on whether
> GENERIC_SCHED_CLOCK is present.  The new approach removes code under
> arch/* since the difference is tied more to the specifics of the Linux
> implementation than to the architecture.
> 
> No functional change.
> 
> Signed-off-by: Michael Kelley <mikelley@...rosoft.com>

Reviewed-by: Boqun Feng <boqun.feng@...il.com>

Regards,
Boqun

> ---
>  arch/x86/include/asm/mshyperv.h    | 11 -----------
>  drivers/clocksource/hyperv_timer.c | 21 +++++++++++++++++++++
>  2 files changed, 21 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index ed9dc56..5ccbba8 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -29,17 +29,6 @@ static inline u64 hv_get_register(unsigned int reg)
>  
>  #define hv_get_raw_timer() rdtsc_ordered()
>  
> -/*
> - * Reference to pv_ops must be inline so objtool
> - * detection of noinstr violations can work correctly.
> - */
> -static __always_inline void hv_setup_sched_clock(void *sched_clock)
> -{
> -#ifdef CONFIG_PARAVIRT
> -	pv_ops.time.sched_clock = sched_clock;
> -#endif
> -}
> -
>  void hyperv_vector_handler(struct pt_regs *regs);
>  
>  static inline void hv_enable_stimer0_percpu_irq(int irq) {}
> diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> index 9cee6db..a2bee50 100644
> --- a/drivers/clocksource/hyperv_timer.c
> +++ b/drivers/clocksource/hyperv_timer.c
> @@ -423,6 +423,27 @@ static u64 notrace read_hv_sched_clock_msr(void)
>  	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
>  };
>  
> +/*
> + * Reference to pv_ops must be inline so objtool
> + * detection of noinstr violations can work correctly.
> + */
> +static __always_inline void hv_setup_sched_clock(void *sched_clock)
> +{
> +#ifdef CONFIG_GENERIC_SCHED_CLOCK
> +	/*
> +	 * We're on an architecture with generic sched clock (not x86/x64).
> +	 * The Hyper-V sched clock read function returns nanoseconds, not
> +	 * the normal 100ns units of the Hyper-V synthetic clock.
> +	 */
> +	sched_clock_register(sched_clock, 64, NSEC_PER_SEC);
> +#else
> +#ifdef CONFIG_PARAVIRT
> +	/* We're on x86/x64 *and* using PV ops */
> +	pv_ops.time.sched_clock = sched_clock;
> +#endif
> +#endif
> +}
> +
>  static bool __init hv_init_tsc_clocksource(void)
>  {
>  	u64		tsc_msr;
> -- 
> 1.8.3.1
>