Re: [kvm-unit-tests PATCH 1/1] arm64: microbench: Improve measurement accuracy of tests

[Andrew Jones <andrew.jones@linux.dev>]

Thanks, Heqiong. The patch is looking much better. The only thing missing
now is the patch version. This is v3, so it should have a prefix like this

 [kvm-unit-tests PATCH v3 1/1]

There's no need to respin for that though. afaict you've addressed
Alexandru's comments, but I'll let him take a look before merging.

Thanks,
drew

On Thu, Nov 16, 2023 at 12:53:55PM +0800, heqiong wrote:
> Reducing the impact of the cntvct_el0 register and isb() operation
> on microbenchmark test results to improve testing accuracy and reduce
> latency in test results.
> 
> Signed-off-by: heqiong <heqiong1557@phytium.com.cn>
> ---
>  arm/micro-bench.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/arm/micro-bench.c b/arm/micro-bench.c
> index fbe59d03..22408955 100644
> --- a/arm/micro-bench.c
> +++ b/arm/micro-bench.c
> @@ -24,7 +24,6 @@
>  #include <asm/gic-v3-its.h>
>  #include <asm/timer.h>
>  
> -#define NS_5_SECONDS		(5 * 1000 * 1000 * 1000UL)
>  #define QEMU_MMIO_ADDR		0x0a000008
>  
>  static u32 cntfrq;
> @@ -346,17 +345,21 @@ static void loop_test(struct exit_test *test)
>  		}
>  	}
>  
> -	while (ntimes < test->times && total_ns.ns < NS_5_SECONDS) {
> -		isb();
> -		start = read_sysreg(cntvct_el0);
> +	dsb(ish);
> +	isb();
> +	start = read_sysreg(cntvct_el0);
> +	isb();
> +	while (ntimes < test->times) {
>  		test->exec();
> -		isb();
> -		end = read_sysreg(cntvct_el0);
>  
>  		ntimes++;
> -		total_ticks += (end - start);
> -		ticks_to_ns_time(total_ticks, &total_ns);
>  	}
> +	dsb(ish);
> +	isb();
> +	end = read_sysreg(cntvct_el0);
> +
> +	total_ticks = end - start;
> +	ticks_to_ns_time(total_ticks, &total_ns);
>  
>  	if (test->post) {
>  		test->post(ntimes, &total_ticks);
> -- 
> 2.39.3
>