Re: [PATCH] perf test: Skip perf bench breakpoint run if no breakpoints available

["Naveen N Rao" <naveen@kernel.org>]

Hi Kajol,

On Wed Aug 23, 2023 at 1:21 PM IST, Kajol Jain wrote:
> Based on commit 7d54a4acd8c1 ("perf test: Skip watchpoint
> tests if no watchpoints available"), hardware breakpoints
> are not available for power9 platform and because of that
> perf bench breakpoint run fails on power9 platform.
> Add code to check for the return value of perf_event_open()
> in breakpoint run and skip the perf bench breakpoint run,
> if hardware breakpoints are not available.
>
> Result on power9 system before patch changes:
> [command]# perf bench breakpoint thread
> perf_event_open: No such device
>
> Result on power9 system after patch changes:
> [command]# ./perf bench breakpoint thread
> Skipping perf bench breakpoint thread: No hardware support
>
> Reported-by: Disha Goel <disgoel@linux.vnet.ibm.com>
> Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
> ---
>  tools/perf/bench/breakpoint.c | 24 +++++++++++++++++++++---
>  1 file changed, 21 insertions(+), 3 deletions(-)

Thanks for fixing this to not report an error. A minor nit below, but 
otherwise:
Acked-by: Naveen N Rao <naveen@kernel.org>

>
> diff --git a/tools/perf/bench/breakpoint.c b/tools/perf/bench/breakpoint.c
> index 41385f89ffc7..dfd18f5db97d 100644
> --- a/tools/perf/bench/breakpoint.c
> +++ b/tools/perf/bench/breakpoint.c
> @@ -47,6 +47,7 @@ struct breakpoint {
>  static int breakpoint_setup(void *addr)
>  {
>  	struct perf_event_attr attr = { .size = 0, };
> +	int fd;
>  
>  	attr.type = PERF_TYPE_BREAKPOINT;
>  	attr.size = sizeof(attr);
> @@ -56,7 +57,12 @@ static int breakpoint_setup(void *addr)
>  	attr.bp_addr = (unsigned long)addr;
>  	attr.bp_type = HW_BREAKPOINT_RW;
>  	attr.bp_len = HW_BREAKPOINT_LEN_1;
> -	return syscall(SYS_perf_event_open, &attr, 0, -1, -1, 0);
> +	fd = syscall(SYS_perf_event_open, &attr, 0, -1, -1, 0);
> +
> +	if (fd < 0)
> +		fd = -errno;
> +
> +	return fd;
>  }
>  
>  static void *passive_thread(void *arg)
> @@ -122,8 +128,14 @@ int bench_breakpoint_thread(int argc, const char **argv)
>  
>  	for (i = 0; i < thread_params.nbreakpoints; i++) {
>  		breakpoints[i].fd = breakpoint_setup(&breakpoints[i].watched);
> -		if (breakpoints[i].fd == -1)
> +
> +		if (breakpoints[i].fd < 0) {
> +			if (breakpoints[i].fd == -ENODEV) {
> +				printf("Skipping perf bench breakpoint thread: No hardware support\n");
> +				return 0;

Should we instead do 'exit(0)' here to stop further benchmarks? Perhaps:
  err(EXIT_SUCCESS, "Skipping perf bench breakpoint thread: No hardware support");

EXIT_SUCCESS looks weird, but should help document that this is not an 
error.

> +			}
>  			exit((perror("perf_event_open"), EXIT_FAILURE));
> +		}
>  	}
>  	gettimeofday(&start, NULL);
>  	for (i = 0; i < thread_params.nparallel; i++) {
> @@ -196,8 +208,14 @@ int bench_breakpoint_enable(int argc, const char **argv)
>  		exit(EXIT_FAILURE);
>  	}
>  	fd = breakpoint_setup(&watched);
> -	if (fd == -1)
> +
> +	if (fd < 0) {
> +		if (fd == -ENODEV) {
> +			printf("Skipping perf bench breakpoint enable: No hardware support\n");
> +			return 0;

Here too.

- Naveen

> +		}
>  		exit((perror("perf_event_open"), EXIT_FAILURE));
> +	}
>  	nthreads = enable_params.npassive + enable_params.nactive;
>  	threads = calloc(nthreads, sizeof(threads[0]));
>  	if (!threads)