linux-kernel - Re: [PATCH v2 08/26] selftests/resctrl: Split measure_cache

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Date:   Tue, 28 Nov 2023 14:13:19 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        <linux-kselftest@...r.kernel.org>, Shuah Khan <shuah@...nel.org>,
        "Shaopeng Tan" <tan.shaopeng@...fujitsu.com>,
        Maciej Wieczór-Retman 
        <maciej.wieczor-retman@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 08/26] selftests/resctrl: Split measure_cache_vals()

Hi Ilpo,

On 11/20/2023 3:13 AM, Ilpo Järvinen wrote:
> measure_cache_vals() does a different thing depending on the test case
> that called it:
>   - For CAT, it measures LLC misses through perf.
>   - For CMT, it measures LLC occupancy through resctrl.
> 
> Split these two functionalities into own functions the CAT and CMT
> tests can call directly. Replace passing the struct resctrl_val_param
> parameter with the filename because it's more generic and all those
> functions need out of resctrl_val.
> 
> Co-developed-by: Fenghua Yu <fenghua.yu@...el.com>
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
>  tools/testing/selftests/resctrl/cache.c       | 66 ++++++++++++-------
>  tools/testing/selftests/resctrl/resctrl.h     |  2 +-
>  tools/testing/selftests/resctrl/resctrl_val.c |  2 +-
>  3 files changed, 43 insertions(+), 27 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/cache.c b/tools/testing/selftests/resctrl/cache.c
> index 8aa6d67db978..129d1c293518 100644
> --- a/tools/testing/selftests/resctrl/cache.c
> +++ b/tools/testing/selftests/resctrl/cache.c
> @@ -147,7 +147,7 @@ static int get_llc_occu_resctrl(unsigned long *llc_occupancy)
>   *
>   * Return:		0 on success. non-zero on failure.
>   */
> -static int print_results_cache(char *filename, int bm_pid,
> +static int print_results_cache(const char *filename, int bm_pid,
>  			       unsigned long llc_value)
>  {
>  	FILE *fp;
> @@ -169,35 +169,51 @@ static int print_results_cache(char *filename, int bm_pid,
>  	return 0;
>  }
>  
> -int measure_cache_vals(struct resctrl_val_param *param, int bm_pid)
> +/*
> + * perf_event_measure - Measure perf events
> + * @filename:	Filename for writing the results
> + * @bm_pid:	PID that runs the benchmark
> + *
> + * Measures perf events (e.g., cache misses) and writes the results into
> + * @filename. @bm_pid is written to the results file along with the measured
> + * value.
> + *
> + * Return: =0 on success. <0 on failure.

I do not think this is accurate. It looks like this function returns
the return value of print_results_cache() which returns errno on failure.
If this is the case then I think this proves that returning a
positive integer on failure should be avoided since it just creates
traps.

> + */
> +static int perf_event_measure(const char *filename, int bm_pid)
>  {
> -	unsigned long llc_perf_miss = 0, llc_occu_resc = 0, llc_value = 0;
> +	unsigned long llc_perf_miss = 0;
>  	int ret;
>  
> -	/*
> -	 * Measure cache miss from perf.
> -	 */
> -	if (!strncmp(param->resctrl_val, CAT_STR, sizeof(CAT_STR))) {
> -		ret = get_llc_perf(&llc_perf_miss);
> -		if (ret < 0)
> -			return ret;
> -		llc_value = llc_perf_miss;
> -	}
> +	ret = get_llc_perf(&llc_perf_miss);
> +	if (ret < 0)
> +		return ret;
>  
> -	/*
> -	 * Measure llc occupancy from resctrl.
> -	 */
> -	if (!strncmp(param->resctrl_val, CMT_STR, sizeof(CMT_STR))) {
> -		ret = get_llc_occu_resctrl(&llc_occu_resc);
> -		if (ret < 0)
> -			return ret;
> -		llc_value = llc_occu_resc;
> -	}
> -	ret = print_results_cache(param->filename, bm_pid, llc_value);
> -	if (ret)
> +	ret = print_results_cache(filename, bm_pid, llc_perf_miss);
> +	return ret;
> +}

Perhaps print_results_cache() can be made to return negative error
and this just be "return print_results_cache(...)" and the function
comment be accurate?

> +
> +/*
> + * measure_llc_resctrl - Measure resctrl llc value from resctrl

llc -> LLC

> + * @filename:	Filename for writing the results
> + * @bm_pid:	PID that runs the benchmark
> + *
> + * Measures llc occupancy from resctrl and writes the results into @filename.

llc -> LLC

> + * @bm_pid is written to the results file along with the measured value.
> + *
> + * Return: =0 on success. <0 on failure.

same issue ?


Reinette