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From: Don Zickus on 16 Feb 2010 17:10
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.

Signed-off-by: Don Zickus <dzickus(a)redhat.com>
---
kernel/nmi_watchdog.c | 23 ++++++++++++++++++-----
1 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/kernel/nmi_watchdog.c b/kernel/nmi_watchdog.c
index 633b230..3c75cbf 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;
--
1.6.6.83.gc9a2

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