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Subject[PATCH 2/3] perf record: Enable counters only when kernel is execing subcommand
Date
From: Zhang, Yanmin <yanmin_zhang@linux.intel.com>

'perf record' starts counters before subcommand is execed, so the
statistics is not precise because it includes data of some preparation
steps. I fix it with the patch.

In addition, Change the condition to fork/exec subcommand. If there is a
subcommand parameter, perf always fork/exec it. The usage example is:

# perf record -f -a sleep 10

So this command could collect statistics for 10 seconds precisely. User
still could stop it by CTRL+C. Without the new capability, user could
only input CTRL+C to stop it without precise time clock.

Signed-off-by: Zhang Yanmin <yanmin_zhang@linux.intel.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sheng Yang <sheng@linux.intel.com>
Cc: oerg Roedel <joro@8bytes.org>
Cc: Jes Sorensen <Jes.Sorensen@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: <zhiteng.huang@intel.com>
Cc: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/builtin-record.c | 33 +++++++++++++++------------------
1 files changed, 15 insertions(+), 18 deletions(-)
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 962cdbf..e2b35ad 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -225,7 +225,7 @@ static struct perf_header_attr *get_header_attr(struct perf_event_attr *a, int n
return h_attr;
}

-static void create_counter(int counter, int cpu, pid_t pid, bool forks)
+static void create_counter(int counter, int cpu, pid_t pid)
{
char *filter = filters[counter];
struct perf_event_attr *attr = attrs + counter;
@@ -275,10 +275,10 @@ static void create_counter(int counter, int cpu, pid_t pid, bool forks)
attr->mmap = track;
attr->comm = track;
attr->inherit = inherit;
- attr->disabled = 1;
-
- if (forks)
+ if (target_pid == -1 && !system_wide) {
+ attr->disabled = 1;
attr->enable_on_exec = 1;
+ }

try_again:
fd[nr_cpu][counter] = sys_perf_event_open(attr, pid, cpu, group_fd, 0);
@@ -380,17 +380,15 @@ try_again:
exit(-1);
}
}
-
- ioctl(fd[nr_cpu][counter], PERF_EVENT_IOC_ENABLE);
}

-static void open_counters(int cpu, pid_t pid, bool forks)
+static void open_counters(int cpu, pid_t pid)
{
int counter;

group_fd = -1;
for (counter = 0; counter < nr_counters; counter++)
- create_counter(counter, cpu, pid, forks);
+ create_counter(counter, cpu, pid);

nr_cpu++;
}
@@ -425,7 +423,7 @@ static int __cmd_record(int argc, const char **argv)
int err;
unsigned long waking = 0;
int child_ready_pipe[2], go_pipe[2];
- const bool forks = target_pid == -1 && argc > 0;
+ const bool forks = argc > 0;
char buf;

page_size = sysconf(_SC_PAGE_SIZE);
@@ -496,13 +494,13 @@ static int __cmd_record(int argc, const char **argv)
atexit(atexit_header);

if (forks) {
- pid = fork();
+ child_pid = fork();
if (pid < 0) {
perror("failed to fork");
exit(-1);
}

- if (!pid) {
+ if (!child_pid) {
close(child_ready_pipe[0]);
close(go_pipe[1]);
fcntl(go_pipe[0], F_SETFD, FD_CLOEXEC);
@@ -531,11 +529,6 @@ static int __cmd_record(int argc, const char **argv)
exit(-1);
}

- child_pid = pid;
-
- if (!system_wide)
- target_pid = pid;
-
close(child_ready_pipe[1]);
close(go_pipe[0]);
/*
@@ -548,13 +541,17 @@ static int __cmd_record(int argc, const char **argv)
close(child_ready_pipe[0]);
}

+ if (forks && target_pid == -1 && !system_wide)
+ pid = child_pid;
+ else
+ pid = target_pid;

if ((!system_wide && !inherit) || profile_cpu != -1) {
- open_counters(profile_cpu, target_pid, forks);
+ open_counters(profile_cpu, pid);
} else {
nr_cpus = read_cpu_map();
for (i = 0; i < nr_cpus; i++)
- open_counters(cpumap[i], target_pid, forks);
+ open_counters(cpumap[i], pid);
}

if (file_new) {
--
1.6.2.5


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