perf record: Enable counters only when kernel is execing subcommand

'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>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.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>
LKML-Reference: <1268922965-14774-2-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 18 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 962cdbf44ae9..e2b35ad82a77 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) {