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

* 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


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