linux-kernel - Re: [PATCH 5/7] clocksource/arm_arch_timer: Drop use of static key in arch_timer_reg_read

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Message-ID: <20190408160433.GQ6139@lakrids.cambridge.arm.com>
Date:   Mon, 8 Apr 2019 17:04:34 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Russell King <linux@....linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [PATCH 5/7] clocksource/arm_arch_timer: Drop use of static key
 in arch_timer_reg_read_stable

On Mon, Apr 08, 2019 at 04:49:05PM +0100, Marc Zyngier wrote:
> Let's start with the removal of the arch_timer_read_ool_enabled
> static key in arch_timer_reg_read_stable. IT is not a fast path,

Nit: s/IT/It/

> and we can simplify things a bit.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>

Acked-by: Mark Rutland <mark.rutland@....com>

Mark.

> ---
>  arch/arm64/include/asm/arch_timer.h | 42 +++++++++++++++++++----------
>  1 file changed, 28 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index c3762ffcc933..4a06d46def7e 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -77,23 +77,37 @@ struct arch_timer_erratum_workaround {
>  DECLARE_PER_CPU(const struct arch_timer_erratum_workaround *,
>  		timer_unstable_counter_workaround);
>  
> +/* inline sysreg accessors that make erratum_handler() work */
> +static inline notrace u32 arch_timer_read_cntp_tval_el0(void)
> +{
> +	return read_sysreg(cntp_tval_el0);
> +}
> +
> +static inline notrace u32 arch_timer_read_cntv_tval_el0(void)
> +{
> +	return read_sysreg(cntv_tval_el0);
> +}
> +
> +static inline notrace u64 arch_timer_read_cntpct_el0(void)
> +{
> +	return read_sysreg(cntpct_el0);
> +}
> +
> +static inline notrace u64 arch_timer_read_cntvct_el0(void)
> +{
> +	return read_sysreg(cntvct_el0);
> +}
> +
>  #define arch_timer_reg_read_stable(reg)					\
> -({									\
> -	u64 _val;							\
> -	if (needs_unstable_timer_counter_workaround()) {		\
> -		const struct arch_timer_erratum_workaround *wa;		\
> +	({								\
> +		u64 _val;						\
> +									\
>  		preempt_disable_notrace();				\
> -		wa = __this_cpu_read(timer_unstable_counter_workaround); \
> -		if (wa && wa->read_##reg)				\
> -			_val = wa->read_##reg();			\
> -		else							\
> -			_val = read_sysreg(reg);			\
> +		_val = erratum_handler(read_ ## reg)();			\
>  		preempt_enable_notrace();				\
> -	} else {							\
> -		_val = read_sysreg(reg);				\
> -	}								\
> -	_val;								\
> -})
> +									\
> +		_val;							\
> +	})
>  
>  /*
>   * These register accessors are marked inline so the compiler can
> -- 
> 2.20.1
>