Re: [PATCH] clocksource: riscv_timer: Provide sched_clock

[Palmer Dabbelt]

On Mon, 03 Dec 2018 04:35:24 PST (-0800), anup@xxxxxxxxxxxxxx wrote:
> Currently, we don't have a sched_clock registered for RISC-V systems.
> This means Linux time keeping will use jiffies (running at HZ) as the
> default sched_clock.
>
> To avoid this, we explicity provide sched_clock using RISC-V rdtime
> instruction (similar to riscv_timer clocksource).
>
> Signed-off-by: Anup Patel <anup@xxxxxxxxxxxxxx>
> ---
>  drivers/clocksource/riscv_timer.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/clocksource/riscv_timer.c b/drivers/clocksource/riscv_timer.c
> index 084e97dc10ed..431892200a08 100644
> --- a/drivers/clocksource/riscv_timer.c
> +++ b/drivers/clocksource/riscv_timer.c
> @@ -8,6 +8,7 @@
>  #include <linux/cpu.h>
>  #include <linux/delay.h>
>  #include <linux/irq.h>
> +#include <linux/sched_clock.h>
>  #include <asm/smp.h>
>  #include <asm/sbi.h>
>
> @@ -49,6 +50,11 @@ static unsigned long long riscv_clocksource_rdtime(struct clocksource *cs)
>  	return get_cycles64();
>  }
>
> +static u64 riscv_sched_clock(void)
> +{
> +	return get_cycles64();
> +}
> +
>  static DEFINE_PER_CPU(struct clocksource, riscv_clocksource) = {
>  	.name		= "riscv_clocksource",
>  	.rating		= 300,
> @@ -97,6 +103,9 @@ static int __init riscv_timer_init_dt(struct device_node *n)
>  	cs = per_cpu_ptr(&riscv_clocksource, cpuid);
>  	clocksource_register_hz(cs, riscv_timebase);
>
> +	sched_clock_register(riscv_sched_clock,
> +			BITS_PER_LONG, riscv_timebase);

Shouldn't this just be 64, not BITS_PER_LONG?  We have 64-bit counters on 
RV32I.

> +
>  	error = cpuhp_setup_state(CPUHP_AP_RISCV_TIMER_STARTING,
>  			 "clockevents/riscv/timer:starting",
>  			 riscv_timer_starting_cpu, riscv_timer_dying_cpu);