Subject: Re: [PATCH v2 4/4] tools/perf: Fix perf bench numa testcase to check if CPU used to bind task is online

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Sat, 9 Apr 2022 12:20:52 -0300

Em Wed, Apr 06, 2022 at 11:21:13PM +0530, Athira Rajeev escreveu:
> Perf numa bench test fails with error:
> 
> Testcase:
> ./perf bench numa mem -p 2 -t 1 -P 1024 -C 0,8 -M 1,0 -s 20 -zZq
> --thp  1 --no-data_rand_walk
> 
> Failure snippet:
> <<>>
>  Running 'numa/mem' benchmark:
> 
>  # Running main, "perf bench numa numa-mem -p 2 -t 1 -P 1024 -C 0,8
> -M 1,0 -s 20 -zZq --thp 1 --no-data_rand_walk"
> 
> perf: bench/numa.c:333: bind_to_cpumask: Assertion `!(ret)' failed.
> <<>>
> 
> The Testcases uses CPU’s 0 and 8. In function "parse_setup_cpu_list",
> There is check to see if cpu number is greater than max cpu’s possible
> in the system ie via "if (bind_cpu_0 >= g->p.nr_cpus ||
> bind_cpu_1 >= g->p.nr_cpus) {". But it could happen that system has
> say 48 CPU’s, but only number of online CPU’s is 0-7. Other CPU’s
> are offlined. Since "g->p.nr_cpus" is 48, so function will go ahead
> and set bit for CPU 8 also in cpumask ( td->bind_cpumask).
> 
> bind_to_cpumask function is called to set affinity using
> sched_setaffinity and the cpumask. Since the CPU8 is not present,
> set affinity will fail here with EINVAL. Fix this issue by adding a
> check to make sure that, CPU’s provided in the input argument values
> are online before proceeding further and skip the test. For this,
> include new helper function "is_cpu_online" in
> "tools/perf/util/header.c".
> 
> Since "BIT(x)" definition will get included from header.h, remove
> that from bench/numa.c
> 
> Tested-by: Disha Goel <[email-masked]>
> Signed-off-by: Athira Rajeev <[email-masked]>
> Reported-by: Disha Goel <[email-masked]>
> ---
>  tools/perf/bench/numa.c  |  8 ++++++--
>  tools/perf/util/header.c | 43 ++++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/header.h |  1 +
>  3 files changed, 50 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/bench/numa.c b/tools/perf/bench/numa.c
> index 29e41e32bd88..7992d79b3e41 100644
> --- a/tools/perf/bench/numa.c
> +++ b/tools/perf/bench/numa.c
> @@ -34,6 +34,7 @@
>  #include <linux/numa.h>
>  #include <linux/zalloc.h>
>  
> +#include "../util/header.h"
>  #include <numa.h>
>  #include <numaif.h>
>  
> @@ -616,6 +617,11 @@ static int parse_setup_cpu_list(void)
>  			return -1;
>  		}
>  
> +		if (is_cpu_online(bind_cpu_0) != 1 || is_cpu_online(bind_cpu_1) != 1) {
> +			printf("\nTest not applicable, bind_cpu_0 or bind_cpu_1 is offline\n");
> +			return -1;
> +		}
> +
>  		BUG_ON(bind_cpu_0 < 0 || bind_cpu_1 < 0);
>  		BUG_ON(bind_cpu_0 > bind_cpu_1);
>  
> @@ -786,8 +792,6 @@ static int parse_nodes_opt(const struct option *opt __maybe_unused,
>  	return parse_node_list(arg);
>  }
>  
> -#define BIT(x) (1ul << x)
> -
>  static inline uint32_t lfsr_32(uint32_t lfsr)
>  {
>  	const uint32_t taps = BIT(1) | BIT(5) | BIT(6) | BIT(31);
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 6da12e522edc..3f5fcf5d4b3f 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -983,6 +983,49 @@ static int write_dir_format(struct feat_fd *ff,
>  	return do_write(ff, &data->dir.version, sizeof(data->dir.version));
>  }
>  
> +#define SYSFS "/sys/devices/system/cpu/"

Please use

int sysfs__read_str(const char *entry, char **buf, size_t *sizep)

See how to use it in the smt_on() function at tools/perf/util/smt.c, for
example.

Now looking at the first patches in the series.

- Arnaldo

> +/*
> + * Check whether a CPU is online
> + *
> + * Returns:
> + *     1 -> if CPU is online
> + *     0 -> if CPU is offline
> + *    -1 -> error case
> + */
> +int is_cpu_online(unsigned int cpu)
> +{
> +	char sysfs_cpu[255];
> +	char buf[255];
> +	struct stat statbuf;
> +	size_t len;
> +	int fd;
> +
> +	snprintf(sysfs_cpu, sizeof(sysfs_cpu), SYSFS "cpu%u", cpu);
> +
> +	if (stat(sysfs_cpu, &statbuf) != 0)
> +		return 0;
> +
> +	/*
> +	 * Check if /sys/devices/system/cpu/cpux/online file
> +	 * exists. In kernels without CONFIG_HOTPLUG_CPU, this
> +	 * file won't exist.
> +	 */
> +	snprintf(sysfs_cpu, sizeof(sysfs_cpu), SYSFS "cpu%u/online", cpu);
> +	if (stat(sysfs_cpu, &statbuf) != 0)
> +		return 1;
> +
> +	fd = open(sysfs_cpu, O_RDONLY);
> +	if (fd == -1)
> +		return -1;
> +
> +	len = read(fd, buf, sizeof(buf) - 1);
> +	buf[len] = '\0';
> +	close(fd);
> +
> +	return strtoul(buf, NULL, 16);
> +}
> +
>  #ifdef HAVE_LIBBPF_SUPPORT
>  static int write_bpf_prog_info(struct feat_fd *ff,
>  			       struct evlist *evlist __maybe_unused)
> diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
> index c9e3265832d9..0eb4bc29a5a4 100644
> --- a/tools/perf/util/header.h
> +++ b/tools/perf/util/header.h
> @@ -158,6 +158,7 @@ int do_write(struct feat_fd *fd, const void *buf, size_t size);
>  int write_padded(struct feat_fd *fd, const void *bf,
>  		 size_t count, size_t count_aligned);
>  
> +int is_cpu_online(unsigned int cpu);
>  /*
>   * arch specific callback
>   */
> -- 
> 2.35.1

-- 

- Arnaldo