linux-kernel - Re: [PATCH] clocksource/drivers/riscv: Increase the clock source rating

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Message-ID: <CA+V-a8t6pL-LrtwZzicUzC67yzZgE3hzHH+MNvdj5LuH7g3s6w@mail.gmail.com>
Date:   Wed, 28 Dec 2022 23:29:43 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Albert Ou <aou@...s.berkeley.edu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] clocksource/drivers/riscv: Increase the clock source rating

Hi Samuel,

Thank you for the patch.

On Wed, Dec 28, 2022 at 12:44 AM Samuel Holland <samuel@...lland.org> wrote:
>
> RISC-V provides an architectural clock source via the time CSR. This
> clock source exposes a 64-bit counter synchronized across all CPUs.
> Because it is accessed using a CSR, it is much more efficient to read
> than MMIO clock sources. For example, on the Allwinner D1, reading the
> sun4i timer in a loop takes 131 cycles/iteration, while reading the
> RISC-V time CSR takes only 5 cycles/iteration.
>
> Adjust the RISC-V clock source rating so it is preferred over the
> various platform-specific MMIO clock sources.
>
> Signed-off-by: Samuel Holland <samuel@...lland.org>
> ---
>
>  drivers/clocksource/timer-riscv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>

Cheers,
Prabhakar

> diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
> index a0d66fabf073..55dad7965f43 100644
> --- a/drivers/clocksource/timer-riscv.c
> +++ b/drivers/clocksource/timer-riscv.c
> @@ -73,7 +73,7 @@ static u64 notrace riscv_sched_clock(void)
>
>  static struct clocksource riscv_clocksource = {
>         .name           = "riscv_clocksource",
> -       .rating         = 300,
> +       .rating         = 400,
>         .mask           = CLOCKSOURCE_MASK(64),
>         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
>         .read           = riscv_clocksource_rdtime,
> --
> 2.37.4
>