linux-kernel - Re: [PATCH v7 6/6] x86/tsc: use tsc early

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Date:   Wed, 8 Nov 2017 17:17:24 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        <steven.sistare@...cle.com>, <daniel.m.jordan@...cle.com>,
        <linux@...linux.org.uk>, <schwidefsky@...ibm.com>,
        <heiko.carstens@...ibm.com>, <john.stultz@...aro.org>,
        <sboyd@...eaurora.org>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
        <tglx@...utronix.de>, <hpa@...or.com>
Subject: Re: [PATCH v7 6/6] x86/tsc: use tsc early

Hi Pavel,

Sorry to reply so late.

I have tested it based on tip tree. it is OK for me.

some concerns below.

At 11/03/2017 01:26 AM, Pavel Tatashin wrote:
> tsc_early_init():
> Determines offset, shift and multiplier for the early clock based on the
> TSC frequency.
>
> tsc_early_fini()
> Implement the finish part of early tsc feature, prints message about the
> offset, which can be useful to find out how much time was spent in post and
> boot manager (if TSC starts from 0 during boot)
>
> sched_clock_early():
> TSC based implementation of early clock.
>
> Call tsc_early_init() to initialize early boot time stamps functionality on
> the supported x86 platforms, and call tsc_early_fini() to finish this
> feature after permanent clock has been initialized.
>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
> ---
>  arch/x86/include/asm/tsc.h |  4 +++
>  arch/x86/kernel/setup.c    | 10 ++++--
>  arch/x86/kernel/time.c     |  1 +
>  arch/x86/kernel/tsc.c      | 81 ++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 94 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
> index f5e6f1c417df..6dc9618b24e3 100644
> --- a/arch/x86/include/asm/tsc.h
> +++ b/arch/x86/include/asm/tsc.h
> @@ -50,11 +50,15 @@ extern bool tsc_store_and_check_tsc_adjust(bool bootcpu);
>  extern void tsc_verify_tsc_adjust(bool resume);
>  extern void check_tsc_sync_source(int cpu);
>  extern void check_tsc_sync_target(void);
> +void tsc_early_init(unsigned int khz);
> +void tsc_early_fini(void);
>  #else
>  static inline bool tsc_store_and_check_tsc_adjust(bool bootcpu) { return false; }
>  static inline void tsc_verify_tsc_adjust(bool resume) { }
>  static inline void check_tsc_sync_source(int cpu) { }
>  static inline void check_tsc_sync_target(void) { }
> +static inline void tsc_early_init(unsigned int khz) { }
> +static inline void tsc_early_fini(void) { }
>  #endif
>
>  extern int notsc_setup(char *);
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 0957dd73d127..3df8be642b80 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -822,7 +822,11 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
>  	return 0;
>  }
>
> -static void __init simple_udelay_calibration(void)
> +/*
> + * Initialize early tsc to show early boot timestamps, and also loops_per_jiffy
> + * for udelay
> + */
> +static void __init early_clock_calibration(void)
>  {
>  	unsigned int tsc_khz, cpu_khz;
>  	unsigned long lpj;
> @@ -837,6 +841,8 @@ static void __init simple_udelay_calibration(void)
>  	if (!tsc_khz)
>  		return;
>
> +	tsc_early_init(tsc_khz);
> +
>  	lpj = tsc_khz * 1000;
>  	do_div(lpj, HZ);
>  	loops_per_jiffy = lpj;
> @@ -1049,7 +1055,7 @@ void __init setup_arch(char **cmdline_p)
>  	 */
>  	init_hypervisor_platform();
>
> -	simple_udelay_calibration();
> +	early_clock_calibration();
>
>  	x86_init.resources.probe_roms();
>
> diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c
> index 3104c5304529..838c5980cae4 100644
> --- a/arch/x86/kernel/time.c
> +++ b/arch/x86/kernel/time.c
> @@ -86,6 +86,7 @@ static __init void x86_late_time_init(void)
>  {
>  	x86_init.timers.timer_init();
>  	tsc_init();
> +	tsc_early_fini();

Can we put this into tsc_init(), So we can remove the definitions in
tsc.h

>  }
>
>  /*
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 1c4502a2b7b2..edacd0aa55f5 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -181,6 +181,80 @@ static void set_cyc2ns_scale(unsigned long khz, int cpu, unsigned long long tsc_
>  	local_irq_restore(flags);
>  }
>
> +#ifdef CONFIG_X86_TSC
> +static struct cyc2ns_data  cyc2ns_early;
> +
> +static u64 sched_clock_early(void)

This function is only called during boot time. Should it
be a "__init" function too?


Thanks
	dou.