Re: [RESEND] qemu/timer: Add host ticks function for RISC-V

[Atish Patra <atishp@atishpatra.org>]

On Thu, Sep 7, 2023 at 8:33 PM LIU Zhiwei <zhiwei_liu@linux.alibaba.com> wrote:
>
> From: LIU Zhiwei <lzw194868@alibaba-inc.com>
>
> Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
> ---
>  include/qemu/timer.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/include/qemu/timer.h b/include/qemu/timer.h
> index 9a91cb1248..105767c195 100644
> --- a/include/qemu/timer.h
> +++ b/include/qemu/timer.h
> @@ -979,6 +979,25 @@ static inline int64_t cpu_get_host_ticks(void)
>      return cur - ofs;
>  }
>
> +#elif defined(__riscv) && defined(__riscv_xlen) && __riscv_xlen == 32
> +static inline int64_t cpu_get_host_ticks(void)
> +{
> +    uint32_t lo, hi;
> +    asm volatile("RDCYCLE %0\n\t"
> +                 "RDCYCLEH %1"
> +                 : "=r"(lo), "=r"(hi));
> +    return lo | (uint64_t)hi << 32;
> +}
> +
> +#elif defined(__riscv) && defined(__riscv_xlen) && __riscv_xlen > 32
> +static inline int64_t cpu_get_host_ticks(void)
> +{
> +    int64_t val;
> +
> +    asm volatile("RDCYCLE %0" : "=r"(val));
> +    return val;
> +}
> +

rdcycle won't be accessible from the user space directly in the
future. rdcycle will be accessible via perf similar to other
architectures from the next kernel release [1].

rdtime must be used to compute the host ticks if the host is a riscv.
This is the equivalent of rdtsc in x86.

[1] https://lore.kernel.org/lkml/CAP-5=fVcMg7TL6W_jH61PW6dYMobuTs13d4JDuTAx=mxJ+PNtQ@mail.gmail.com/T/#md852c28f4070212973b796c232ecd37dc1c6cb2b

>  #else
>  /* The host CPU doesn't have an easily accessible cycle counter.
>     Just return a monotonically increasing value.  This will be
> --
> 2.17.1
>
>


-- 
Regards,
Atish