Re: [PATCH v3] perf/sched: fix for getting task's execution time

[Ingo Molnar <mingo@elte.hu>]

* Xiao Guangrong <xiaoguangrong@cn.fujitsu.com> wrote:

> In current code, task's execute time is got by reading
> '/proc/<pid>/sched' file, it's wrong if the task is created
> by pthread_create(), because every thread task has same pid.
> 
> This way also has two demerits:
> 
> 1: 'perf sched replay' can't work if the kernel not compile
>     with 'CONFIG_SCHED_DEBUG' option
> 2: perf tool should depend on proc file system
> 
> So, this patch use PERF_COUNT_SW_TASK_CLOCK to get task's
> execution time instead of reading /proc file
> 
> Changelog v2 -> v3:
> use PERF_COUNT_SW_TASK_CLOCK instead of rusage() as Ingo's suggestion
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
> ---
>  tools/perf/builtin-sched.c |   55 +++++++++++++++++++++----------------------
>  1 files changed, 27 insertions(+), 28 deletions(-)
> 
> diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
> index 19f43fa..b12b23a 100644
> --- a/tools/perf/builtin-sched.c
> +++ b/tools/perf/builtin-sched.c
> @@ -13,7 +13,6 @@
>  #include "util/debug.h"
>  #include "util/data_map.h"
>  
> -#include <sys/types.h>
>  #include <sys/prctl.h>
>  
>  #include <semaphore.h>
> @@ -414,34 +413,33 @@ static u64 get_cpu_usage_nsec_parent(void)
>  	return sum;
>  }
>  
> -static u64 get_cpu_usage_nsec_self(void)
> +static int self_open_counters(void)
>  {
> -	char filename [] = "/proc/1234567890/sched";
> -	unsigned long msecs, nsecs;
> -	char *line = NULL;
> -	u64 total = 0;
> -	size_t len = 0;
> -	ssize_t chars;
> -	FILE *file;
> -	int ret;
> +	struct perf_event_attr attr;
> +	int fd;
>  
> -	sprintf(filename, "/proc/%d/sched", getpid());
> -	file = fopen(filename, "r");
> -	BUG_ON(!file);
> +	memset(&attr, 0, sizeof(attr));
>  
> -	while ((chars = getline(&line, &len, file)) != -1) {
> -		ret = sscanf(line, "se.sum_exec_runtime : %ld.%06ld\n",
> -			&msecs, &nsecs);
> -		if (ret == 2) {
> -			total = msecs*1e6 + nsecs;
> -			break;
> -		}
> -	}
> -	if (line)
> -		free(line);
> -	fclose(file);
> +	attr.type = PERF_TYPE_SOFTWARE;
> +	attr.config = PERF_COUNT_SW_TASK_CLOCK;
>  
> -	return total;
> +	fd = sys_perf_event_open(&attr, 0, -1, -1, 0);
> +
> +	if (fd < 0)
> +		die("Error: sys_perf_event_open() syscall returned"
> +		    "with %d (%s)\n", fd, strerror(errno));
> +	return fd;
> +}
> +
> +static u64 get_cpu_usage_nsec_self(int fd)
> +{
> +	u64 runtime;
> +	int ret;
> +
> +	ret = read(fd, &runtime, sizeof(runtime));
> +	BUG_ON(ret != sizeof(runtime));
> +
> +	return runtime;
>  }
>  
>  static void *thread_func(void *ctx)
> @@ -450,9 +448,11 @@ static void *thread_func(void *ctx)
>  	u64 cpu_usage_0, cpu_usage_1;
>  	unsigned long i, ret;
>  	char comm2[22];
> +	int fd;
>  
>  	sprintf(comm2, ":%s", this_task->comm);
>  	prctl(PR_SET_NAME, comm2);
> +	fd = self_open_counters();
>  
>  again:
>  	ret = sem_post(&this_task->ready_for_work);
> @@ -462,16 +462,15 @@ again:
>  	ret = pthread_mutex_unlock(&start_work_mutex);
>  	BUG_ON(ret);
>  
> -	cpu_usage_0 = get_cpu_usage_nsec_self();
> +	cpu_usage_0 = get_cpu_usage_nsec_self(fd);
>  
>  	for (i = 0; i < this_task->nr_events; i++) {
>  		this_task->curr_event = i;
>  		process_sched_event(this_task, this_task->atoms[i]);
>  	}
>  
> -	cpu_usage_1 = get_cpu_usage_nsec_self();
> +	cpu_usage_1 = get_cpu_usage_nsec_self(fd);
>  	this_task->cpu_usage = cpu_usage_1 - cpu_usage_0;
> -
>  	ret = sem_post(&this_task->work_done_sem);
>  	BUG_ON(ret);

Very nice - and the code even got shorter a tiny bit.

Applied, thanks!

	Ingo