Re: [PATCH v3 2/6] perf tsc: Add rdtsc() for Arm64

[peterz]

On Wed, Sep 02, 2020 at 02:21:27PM +0100, Leo Yan wrote:
> The system register CNTVCT_EL0 can be used to retrieve the counter from
> user space.  Add rdtsc() for Arm64.

> +u64 rdtsc(void)
> +{
> +	u64 val;

Would it make sense to put a comment in that this counter is/could-be
'short' ? Because unlike x86-TSC, this thing isn't architecturally
specified to be 64bits wide.

> +	asm volatile("mrs %0, cntvct_el0" : "=r" (val));
> +
> +	return val;
> +}
> -- 
> 2.17.1
>