perf top: Fall back to cpu-clock-tick hrtimer sampling if no cycle counter available

On architectures/CPUs without PMU support but with perfcounters
enabled 'perf top' 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
is 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, 68 insertions, 45 deletions

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index fdc1d5863b01..6da30a140e86 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -527,58 +527,81 @@ static void mmap_read(void)
         }
 }
 
-static int __cmd_top(void)
+int nr_poll;
+int group_fd;
+
+static void start_counter(int i, int counter)
 {
         struct perf_counter_attr *attr;
-        pthread_t thread;
-        int i, counter, group_fd, nr_poll = 0;
         unsigned int cpu;
+
+        cpu = profile_cpu;
+        if (target_pid == -1 && profile_cpu == -1)
+                cpu = i;
+
+        attr = attrs + counter;
+
+        attr->sample_type       = PERF_SAMPLE_IP | PERF_SAMPLE_TID;
+        attr->freq              = freq;
+
+try_again:
+        fd[i][counter] = sys_perf_counter_open(attr, target_pid, cpu, group_fd, 0);
+
+        if (fd[i][counter] < 0) {
+                int err = errno;
+
+                error("sys_perf_counter_open() syscall returned with %d (%s)\n",
+                        fd[i][counter], strerror(err));
+
+                if (err == EPERM)
+                        die(" No permission - 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) {
+
+                        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[i][counter] >= 0);
+        fcntl(fd[i][counter], F_SETFL, O_NONBLOCK);
+
+        /*
+         * First counter acts as the group leader:
+         */
+        if (group && group_fd == -1)
+                group_fd = fd[i][counter];
+
+        event_array[nr_poll].fd = fd[i][counter];
+        event_array[nr_poll].events = POLLIN;
+        nr_poll++;
+
+        mmap_array[i][counter].counter = counter;
+        mmap_array[i][counter].prev = 0;
+        mmap_array[i][counter].mask = mmap_pages*page_size - 1;
+        mmap_array[i][counter].base = mmap(NULL, (mmap_pages+1)*page_size,
+                        PROT_READ, MAP_SHARED, fd[i][counter], 0);
+        if (mmap_array[i][counter].base == MAP_FAILED)
+                die("failed to mmap with %d (%s)\n", errno, strerror(errno));
+}
+
+static int __cmd_top(void)
+{
+        pthread_t thread;
+        int i, counter;
         int ret;
 
         for (i = 0; i < nr_cpus; i++) {
                 group_fd = -1;
-                for (counter = 0; counter < nr_counters; counter++) {
-
-                        cpu     = profile_cpu;
-                        if (target_pid == -1 && profile_cpu == -1)
-                                cpu = i;
-
-                        attr = attrs + counter;
-
-                        attr->sample_type       = PERF_SAMPLE_IP | PERF_SAMPLE_TID;
-                        attr->freq              = freq;
-
-                        fd[i][counter] = sys_perf_counter_open(attr, target_pid, cpu, group_fd, 0);
-                        if (fd[i][counter] < 0) {
-                                int err = errno;
-
-                                error("syscall returned with %d (%s)\n",
-                                        fd[i][counter], strerror(err));
-                                if (err == EPERM)
-                                        printf("Are you root?\n");
-                                exit(-1);
-                        }
-                        assert(fd[i][counter] >= 0);
-                        fcntl(fd[i][counter], F_SETFL, O_NONBLOCK);
-
-                        /*
-                         * First counter acts as the group leader:
-                         */
-                        if (group && group_fd == -1)
-                                group_fd = fd[i][counter];
-
-                        event_array[nr_poll].fd = fd[i][counter];
-                        event_array[nr_poll].events = POLLIN;
-                        nr_poll++;
-
-                        mmap_array[i][counter].counter = counter;
-                        mmap_array[i][counter].prev = 0;
-                        mmap_array[i][counter].mask = mmap_pages*page_size - 1;
-                        mmap_array[i][counter].base = mmap(NULL, (mmap_pages+1)*page_size,
-                                        PROT_READ, MAP_SHARED, fd[i][counter], 0);
-                        if (mmap_array[i][counter].base == MAP_FAILED)
-                                die("failed to mmap with %d (%s)\n", errno, strerror(errno));
-                }
+                for (counter = 0; counter < nr_counters; counter++)
+                        start_counter(i, counter);
         }
 
         /* Wait for a minimal set of events before starting the snapshot */