On Wed, 8 Jan 2014, Peter Zijlstra wrote:
> On Wed, Jan 08, 2014 at 04:28:20PM -0500, Vince Weaver wrote:
> > Should the perf_event interface handle setups like this better and work
> > fine in aggregate mode but return ENOTSUP if a sampled or overflow event
> > is attempted?
>
> Yeah that would be better, we do something similar for P6 class machines
> without lapic IIRC.
You're right. Something like the following works for me on the rasp-pi,
although maybe if x86 is doing it too things should be moved up into
generic code?
---
Return EOPNOTSUPP if we have no PMU overflow interrupt but a
sampled event is requested.
Signed-off-by: Vince Weaver <vincent.wea...@maine.edu>
diff --git a/arch/arm/include/asm/pmu.h b/arch/arm/include/asm/pmu.h
index f24edad..f1f27a3 100644
--- a/arch/arm/include/asm/pmu.h
+++ b/arch/arm/include/asm/pmu.h
@@ -87,6 +87,7 @@ struct arm_pmu {
u64 max_period;
struct platform_device *plat_device;
struct pmu_hw_events *(*get_hw_events)(void);
+ int no_overflow_interrupt;
};
#define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))
diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index bc3f2ef..fa4ecc3 100644
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -397,7 +397,7 @@ __hw_perf_event_init(struct perf_event *event)
*/
hwc->config_base |= (unsigned long)mapping;
- if (!hwc->sample_period) {
+ if (!is_sampling_event(event)) {
/*
* For non-sampling runs, limit the sample_period to half
* of the counter width. That way, the new counter value
@@ -407,6 +407,12 @@ __hw_perf_event_init(struct perf_event *event)
hwc->sample_period = armpmu->max_period >> 1;
hwc->last_period = hwc->sample_period;
local64_set(&hwc->period_left, hwc->sample_period);
+ } else {
+ /*
+ * If we have no PMU interrupt we cannot sample
+ */
+ if (armpmu->no_overflow_interrupt)
+ return -EOPNOTSUPP;
}
if (event->group_leader != event) {
diff --git a/arch/arm/kernel/perf_event_cpu.c b/arch/arm/kernel/perf_event_cpu.c
index d85055c..a74e0cd 100644
--- a/arch/arm/kernel/perf_event_cpu.c
+++ b/arch/arm/kernel/perf_event_cpu.c
@@ -97,8 +97,9 @@ static int cpu_pmu_request_irq(struct arm_pmu *cpu_pmu,
irq_handler_t handler)
irqs = min(pmu_device->num_resources, num_possible_cpus());
if (irqs < 1) {
- pr_err("no irqs for PMUs defined\n");
- return -ENODEV;
+ printk_once("no irqs for PMUs defined, emulating with
hrtimer\n");
+ cpu_pmu->no_overflow_interrupt=1;
+ return 0;
}
for (i = 0; i < irqs; ++i) {
--
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