Re: [PATCH 1/2] x86/tsc: Avoid a double call if TSC initializes earlier.

From: Pavel Tatashin
Date: Mon Jul 30 2018 - 10:09:49 EST


On Mon, Jul 30, 2018 at 3:55 AM Dou Liyang <douly.fnst@xxxxxxxxxxxxxx> wrote:
>
> static_branch_enable(&__use_tsc) may be called twice in common case, that
> is redundant. And there are also some common functions both in
> tsc_early_init() and tsc_init().
>
> Move them into a separate helper function, only call it once.
> Also fix comments:
> -s/authorative/authoritative
> -s/cyc2ns_init/tsc_init
>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Signed-off-by: Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>

Hi Dou,

Nice cleanup.
Reviewed-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>

Thank you,
Pavel

> ---
> arch/x86/kernel/tsc.c | 22 ++++++++++++----------
> 1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 02e416b87ac1..ba0a6b6e0726 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -182,7 +182,7 @@ static void __init cyc2ns_init_boot_cpu(void)
> }
>
> /*
> - * Secondary CPUs do not run through cyc2ns_init(), so set up
> + * Secondary CPUs do not run through tsc_init(), so set up
> * all the scale factors for all CPUs, assuming the same
> * speed as the bootup CPU. (cpufreq notifiers will fix this
> * up if their speed diverges)
> @@ -1389,7 +1389,7 @@ static bool __init determine_cpu_tsc_frequencies(bool early)
> }
>
> /*
> - * Trust non-zero tsc_khz as authorative,
> + * Trust non-zero tsc_khz as authoritative,
> * and use it to sanity check cpu_khz,
> * which will be off if system timer is off.
> */
> @@ -1421,6 +1421,14 @@ static unsigned long __init get_loops_per_jiffy(void)
> return lpj;
> }
>
> +static void __init enable_use_tsc(void)
> +{
> + /* Sanitize TSC ADJUST before cyc2ns gets initialized */
> + tsc_store_and_check_tsc_adjust(true);
> + cyc2ns_init_boot_cpu();
> + static_branch_enable(&__use_tsc);
> +}
> +
> void __init tsc_early_init(void)
> {
> if (!boot_cpu_has(X86_FEATURE_TSC))
> @@ -1429,10 +1437,7 @@ void __init tsc_early_init(void)
> return;
> loops_per_jiffy = get_loops_per_jiffy();
>
> - /* Sanitize TSC ADJUST before cyc2ns gets initialized */
> - tsc_store_and_check_tsc_adjust(true);
> - cyc2ns_init_boot_cpu();
> - static_branch_enable(&__use_tsc);
> + enable_use_tsc();
> }
>
> void __init tsc_init(void)
> @@ -1456,13 +1461,10 @@ void __init tsc_init(void)
> setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
> return;
> }
> - /* Sanitize TSC ADJUST before cyc2ns gets initialized */
> - tsc_store_and_check_tsc_adjust(true);
> - cyc2ns_init_boot_cpu();
> + enable_use_tsc();
> }
>
> cyc2ns_init_secondary_cpus();
> - static_branch_enable(&__use_tsc);
>
> if (!no_sched_irq_time)
> enable_sched_clock_irqtime();
> --
> 2.14.3
>
>
>