linux-kernel - Re: [PATCH 10/24] selftests/resctrl: Remove nested calls in perf event handling

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Message-ID: <93113f94-9663-4cbb-962f-c415bc975f12@intel.com>
Date:   Thu, 2 Nov 2023 10:49:26 -0700
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 10/24] selftests/resctrl: Remove nested calls in perf
 event handling

Hi Ilpo,

On 10/24/2023 2:26 AM, Ilpo Järvinen wrote:
> Perf event handling has functions that are the sole caller of another
> perf event handling related function:
>   - reset_enable_llc_perf() calls perf_event_open_llc_miss()
>   - reset_enable_llc_perf() calls ioctl_perf_event_ioc_reset_enable()
>   - measure_llc_perf() calls get_llc_perf()
> 
> Remove the extra layer of calls to make the code easier to follow by
> moving the code into the calling function.
> 
> In addition, converts print_results_cache() unsigned long parameter to
> __u64 that matches the type coming from perf.

Is this referring to work from previous patch?

> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
>  tools/testing/selftests/resctrl/cache.c | 86 +++++++------------------
>  1 file changed, 25 insertions(+), 61 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/cache.c b/tools/testing/selftests/resctrl/cache.c
> index d39ef4eebc37..208af1ecae28 100644
> --- a/tools/testing/selftests/resctrl/cache.c
> +++ b/tools/testing/selftests/resctrl/cache.c
> @@ -29,25 +29,6 @@ static void initialize_perf_event_attr(void)
>  	pea_llc_miss.disabled = 1;
>  }
>  
> -static void ioctl_perf_event_ioc_reset_enable(void)
> -{
> -	ioctl(fd_lm, PERF_EVENT_IOC_RESET, 0);
> -	ioctl(fd_lm, PERF_EVENT_IOC_ENABLE, 0);
> -}
> -
> -static int perf_event_open_llc_miss(pid_t pid, int cpu_no)
> -{
> -	fd_lm = perf_event_open(&pea_llc_miss, pid, cpu_no, -1,
> -				PERF_FLAG_FD_CLOEXEC);
> -	if (fd_lm == -1) {
> -		perror("Error opening leader");
> -		ctrlc_handler(0, NULL, NULL);
> -		return -1;
> -	}
> -
> -	return 0;
> -}
> -
>  static void initialize_llc_perf(void)
>  {
>  	memset(&pea_llc_miss, 0, sizeof(struct perf_event_attr));
> @@ -63,42 +44,16 @@ static void initialize_llc_perf(void)
>  
>  static int reset_enable_llc_perf(pid_t pid, int cpu_no)
>  {
> -	int ret = 0;
> -
> -	ret = perf_event_open_llc_miss(pid, cpu_no);
> -	if (ret < 0)
> -		return ret;
> -
> -	/* Start counters to log values */
> -	ioctl_perf_event_ioc_reset_enable();
> -
> -	return 0;
> -}
> -
> -/*
> - * get_llc_perf:	llc cache miss through perf events
> - * @llc_perf_miss:	LLC miss counter that is filled on success
> - *
> - * Perf events like HW_CACHE_MISSES could be used to validate number of
> - * cache lines allocated.
> - *
> - * Return: =0 on success.  <0 on failure.
> - */
> -static int get_llc_perf(__u64 *llc_perf_miss)
> -{
> -	int ret;
> -
> -	/* Stop counters after one span to get miss rate */
> -
> -	ioctl(fd_lm, PERF_EVENT_IOC_DISABLE, 0);
> -
> -	ret = read(fd_lm, &rf_cqm, sizeof(struct read_format));
> -	if (ret == -1) {
> -		perror("Could not get llc misses through perf");
> +	fd_lm = perf_event_open(&pea_llc_miss, pid, cpu_no, -1, PERF_FLAG_FD_CLOEXEC);
> +	if (fd_lm == -1) {
> +		perror("Error opening leader");
> +		ctrlc_handler(0, NULL, NULL);

I understand you just copied the code here ... but it is not clear to me
why this particular error handling deserves a ctrlc_handler().

>  		return -1;
>  	}
>  
> -	*llc_perf_miss = rf_cqm.values[0].value;
> +	/* Start counters to log values */
> +	ioctl(fd_lm, PERF_EVENT_IOC_RESET, 0);
> +	ioctl(fd_lm, PERF_EVENT_IOC_ENABLE, 0);
>  
>  	return 0;
>  }
> @@ -166,20 +121,29 @@ static int print_results_cache(char *filename, int bm_pid, __u64 llc_value)
>  	return 0;
>  }
>  
> +/*
> + * measure_llc_perf:	measure perf events
> + * @bm_pid:	child pid that runs benchmark

I expected "bm_pid" to reflect a "benchmark pid" that
is not unique to the child. Are both parent and child
not running the benchmark?

Missing doc of a parameter here.

> + *
> + * Measure things like cache misses from perf events.

"things like cache misses" is vague. The function's name 
still contains "llc" which makes me think it is not quite
generic yet.



> + *
> + * Return: =0 on success.  <0 on failure.
> + */
>  static int measure_llc_perf(struct resctrl_val_param *param, int bm_pid)
>  {
> -	__u64 llc_perf_miss = 0;
>  	int ret;
>  
> -	/*
> -	 * Measure cache miss from perf.
> -	 */
> -	ret = get_llc_perf(&llc_perf_miss);
> -	if (ret < 0)
> -		return ret;
> +	/* Stop counters after one span to get miss rate */
> +	ioctl(fd_lm, PERF_EVENT_IOC_DISABLE, 0);
>  
> -	ret = print_results_cache(param->filename, bm_pid, llc_perf_miss);
> -	return ret;
> +	ret = read(fd_lm, &rf_cqm, sizeof(struct read_format));
> +	close(fd_lm);

I am not able to tell where this close() moved from.

> +	if (ret == -1) {
> +		perror("Could not get perf value");
> +		return -1;
> +	}
> +
> +	return print_results_cache(param->filename, bm_pid, rf_cqm.values[0].value);
>  }
>  
>  int measure_llc_resctrl(struct resctrl_val_param *param, int bm_pid)

Reinette