nmi_watchdog: Properly configure for software events

Paul Mackerras brought up a good point that when fallbacking to
software events, I may have been lucky in my configuration.

Modified the code to explicit provide a new configuration for
software events.

Suggested-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: gorcunov@gmail.com
Cc: aris@redhat.com
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1266357745-26671-1-git-send-email-dzickus@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 18 insertions, 5 deletions

diff --git a/kernel/nmi_watchdog.c b/kernel/nmi_watchdog.c
index 633b230c2319..3c75cbf3acb8 100644
--- a/kernel/nmi_watchdog.c
+++ b/kernel/nmi_watchdog.c
@@ -61,7 +61,7 @@ static int __init setup_nmi_watchdog(char *str)
 }
 __setup("nmi_watchdog=", setup_nmi_watchdog);
 
-struct perf_event_attr wd_attr = {
+struct perf_event_attr wd_hw_attr = {
         .type = PERF_TYPE_HARDWARE,
         .config = PERF_COUNT_HW_CPU_CYCLES,
         .size = sizeof(struct perf_event_attr),
@@ -69,6 +69,14 @@ struct perf_event_attr wd_attr = {
         .disabled = 1,
 };
 
+struct perf_event_attr wd_sw_attr = {
+        .type = PERF_TYPE_SOFTWARE,
+        .config = PERF_COUNT_SW_CPU_CLOCK,
+        .size = sizeof(struct perf_event_attr),
+        .pinned = 1,
+        .disabled = 1,
+};
+
 void wd_overflow(struct perf_event *event, int nmi,
                  struct perf_sample_data *data,
                  struct pt_regs *regs)
@@ -105,6 +113,7 @@ void wd_overflow(struct perf_event *event, int nmi,
 static int enable_nmi_watchdog(int cpu)
 {
         struct perf_event *event;
+        struct perf_event_attr *wd_attr;
 
         event = per_cpu(nmi_watchdog_ev, cpu);
         if (event && event->state > PERF_EVENT_STATE_OFF)
@@ -112,11 +121,15 @@ static int enable_nmi_watchdog(int cpu)
 
         if (event == NULL) {
                 /* Try to register using hardware perf events first */
-                wd_attr.sample_period = hw_nmi_get_sample_period();
-                event = perf_event_create_kernel_counter(&wd_attr, cpu, -1, wd_overflow);
+                wd_attr = &wd_hw_attr;
+                wd_attr->sample_period = hw_nmi_get_sample_period();
+                event = perf_event_create_kernel_counter(wd_attr, cpu, -1, wd_overflow);
                 if (IS_ERR(event)) {
-                        wd_attr.type = PERF_TYPE_SOFTWARE;
-                        event = perf_event_create_kernel_counter(&wd_attr, cpu, -1, wd_overflow);
+                        /* hardware doesn't exist or not supported, fallback to software events */
+                        printk("nmi_watchdog: hardware not available, trying software events\n");
+                        wd_attr = &wd_sw_attr;
+                        wd_attr->sample_period = NSEC_PER_SEC;
+                        event = perf_event_create_kernel_counter(wd_attr, cpu, -1, wd_overflow);
                         if (IS_ERR(event)) {
                                 printk(KERN_ERR "nmi watchdog failed to create perf event on %i: %p\n", cpu, event);
                                 return -1;