Re: [PATCH V2 06/13] selftests/resctrl: Remove "once" parameter required to be false

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Thu, 12 Sep 2024, Reinette Chatre wrote:

> The CMT, MBM, and MBA tests rely on a benchmark that runs while
> the test makes changes to needed configuration (for example memory
> bandwidth allocation) and takes needed measurements. By default
> the "fill_buf" benchmark is used and by default (via its
> "once = false" setting) "fill_buf" is configured to run until
> terminated after the test completes.
> 
> An unintended consequence of enabling the user to override the
> benchmark also enables the user to change parameters to the
> "fill_buf" benchmark. This enables the user to set "fill_buf" to
> only cycle through the buffer once (by setting "once = true")
> and thus breaking the CMT, MBA, and MBM tests that expect
> workload/interference to be reflected by their measurements.
> 
> Prevent user space from changing the "once" parameter and ensure
> that it is always false for the CMT, MBA, and MBM tests.
> 
> Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
> Changes since V1:
> - New patch
> ---
>  tools/testing/selftests/resctrl/fill_buf.c      |  7 ++++---
>  tools/testing/selftests/resctrl/resctrl.h       |  2 +-
>  tools/testing/selftests/resctrl/resctrl_tests.c |  8 +++++++-
>  tools/testing/selftests/resctrl/resctrl_val.c   | 11 +----------
>  4 files changed, 13 insertions(+), 15 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c
> index 34e5df721430..854f0108d8e6 100644
> --- a/tools/testing/selftests/resctrl/fill_buf.c
> +++ b/tools/testing/selftests/resctrl/fill_buf.c
> @@ -151,7 +151,7 @@ unsigned char *alloc_buffer(size_t buf_size, int memflush)
>  	return buf;
>  }
>  
> -int run_fill_buf(size_t buf_size, int memflush, int op, bool once)
> +int run_fill_buf(size_t buf_size, int memflush, int op)
>  {
>  	unsigned char *buf;
>  
> @@ -160,9 +160,10 @@ int run_fill_buf(size_t buf_size, int memflush, int op, bool once)
>  		return -1;
>  
>  	if (op == 0)
> -		fill_cache_read(buf, buf_size, once);
> +		fill_cache_read(buf, buf_size, false);
>  	else
> -		fill_cache_write(buf, buf_size, once);
> +		fill_cache_write(buf, buf_size, false);
> +
>  	free(buf);
>  
>  	return 0;
> diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
> index 2dda56084588..51f5f4b25e06 100644
> --- a/tools/testing/selftests/resctrl/resctrl.h
> +++ b/tools/testing/selftests/resctrl/resctrl.h
> @@ -142,7 +142,7 @@ int perf_event_open(struct perf_event_attr *hw_event, pid_t pid, int cpu,
>  unsigned char *alloc_buffer(size_t buf_size, int memflush);
>  void mem_flush(unsigned char *buf, size_t buf_size);
>  void fill_cache_read(unsigned char *buf, size_t buf_size, bool once);
> -int run_fill_buf(size_t buf_size, int memflush, int op, bool once);
> +int run_fill_buf(size_t buf_size, int memflush, int op);
>  int initialize_mem_bw_imc(void);
>  int measure_mem_bw(const struct user_params *uparams,
>  		   struct resctrl_val_param *param, pid_t bm_pid,
> diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
> index ecbb7605a981..bee4123a5a9b 100644
> --- a/tools/testing/selftests/resctrl/resctrl_tests.c
> +++ b/tools/testing/selftests/resctrl/resctrl_tests.c
> @@ -266,7 +266,13 @@ int main(int argc, char **argv)
>  		uparams.benchmark_cmd[1] = span_str;
>  		uparams.benchmark_cmd[2] = "1";
>  		uparams.benchmark_cmd[3] = "0";
> -		uparams.benchmark_cmd[4] = "false";
> +		/*
> +		 * Fourth parameter was previously used to indicate
> +		 * how long "fill_buf" should run for, with "false"
> +		 * ("fill_buf" will keep running until terminated)
> +		 * the only option that works.
> +		 */
> +		uparams.benchmark_cmd[4] = NULL;
>  		uparams.benchmark_cmd[5] = NULL;

Why is the [5] assignment kept around? Is something depending on this 
double NULL termination? This patch removed the access to [4] so I 
don't see anything beyong [3] accessed explicitly.

-- 
 i.

>  	}
>  
> diff --git a/tools/testing/selftests/resctrl/resctrl_val.c b/tools/testing/selftests/resctrl/resctrl_val.c
> index e88d5ca30517..5331354aaf64 100644
> --- a/tools/testing/selftests/resctrl/resctrl_val.c
> +++ b/tools/testing/selftests/resctrl/resctrl_val.c
> @@ -625,7 +625,6 @@ static void run_benchmark(int signum, siginfo_t *info, void *ucontext)
>  	int operation, ret, memflush;
>  	char **benchmark_cmd;
>  	size_t span;
> -	bool once;
>  	FILE *fp;
>  
>  	benchmark_cmd = info->si_ptr;
> @@ -645,16 +644,8 @@ static void run_benchmark(int signum, siginfo_t *info, void *ucontext)
>  		span = strtoul(benchmark_cmd[1], NULL, 10);
>  		memflush =  atoi(benchmark_cmd[2]);
>  		operation = atoi(benchmark_cmd[3]);
> -		if (!strcmp(benchmark_cmd[4], "true")) {
> -			once = true;
> -		} else if (!strcmp(benchmark_cmd[4], "false")) {
> -			once = false;
> -		} else {
> -			ksft_print_msg("Invalid once parameter\n");
> -			parent_exit(ppid);
> -		}
>  
> -		if (run_fill_buf(span, memflush, operation, once))
> +		if (run_fill_buf(span, memflush, operation))
>  			fprintf(stderr, "Error in running fill buffer\n");
>  	} else {
>  		/* Execute specified benchmark */
>