perf record: Fall back to cpu-clock-ticks if no PMU

On architectures/CPUs without PMU support but with perfcounters
enabled 'perf record' currently fails because it cannot create a
cycle based hw-perfcounter.

Fall back to the cpu-clock-tick sw-perfcounter in this case, which
is hrtimer based and will always work (as long as perfcounters
are enabled).

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 23 insertions, 2 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index aeab9c4b15e..87866294a0e 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -37,6 +37,7 @@ static pid_t			target_pid			= -1;
 static int                      inherit                         = 1;
 static int                      force                           = 0;
 static int                      append_file                     = 0;
+static int                      verbose                         = 0;
 
 static long                     samples;
 static struct timeval           last_read;
@@ -349,17 +350,35 @@ static void create_counter(int counter, int cpu, pid_t pid)
 
         track = 0; /* only the first counter needs these */
 
+try_again:
         fd[nr_cpu][counter] = sys_perf_counter_open(attr, pid, cpu, group_fd, 0);
 
         if (fd[nr_cpu][counter] < 0) {
                 int err = errno;
 
-                error("syscall returned with %d (%s)\n",
+                if (verbose)
+                        error("sys_perf_counter_open() syscall returned with %d (%s)\n",
                                 fd[nr_cpu][counter], strerror(err));
                 if (err == EPERM)
-                        printf("Are you root?\n");
+                        die("Permission error - are you root?\n");
+
+                /*
+                 * If it's cycles then fall back to hrtimer
+                 * based cpu-clock-tick sw counter, which
+                 * is always available even if no PMU support:
+                 */
+                if (attr->type == PERF_TYPE_HARDWARE
+                        && attr->config == PERF_COUNT_CPU_CYCLES) {
+
+                        if (verbose)
+                                warning(" ... trying to fall back to cpu-clock-ticks\n");
+                        attr->type = PERF_TYPE_SOFTWARE;
+                        attr->config = PERF_COUNT_CPU_CLOCK;
+                        goto try_again;
+                }
                 exit(-1);
         }
+
         assert(fd[nr_cpu][counter] >= 0);
         fcntl(fd[nr_cpu][counter], F_SETFL, O_NONBLOCK);
 
@@ -519,6 +538,8 @@ static const struct option options[] = {
                     "profile at this frequency"),
         OPT_INTEGER('m', "mmap-pages", &mmap_pages,
                     "number of mmap data pages"),
+        OPT_BOOLEAN('v', "verbose", &verbose,
+                    "be more verbose (show counter open errors, etc)"),
         OPT_END()
 };