perf_counter: frequency based adaptive irq_period

Instead of specifying the irq_period for a counter, provide a target interrupt
frequency and dynamically adapt the irq_period to match this frequency.

[ Impact: new perf-counter attribute/feature ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <20090515132018.646195868@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 9 insertions, 13 deletions

diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c
index bb1b463c1361..db8d5cafc159 100644
--- a/arch/powerpc/kernel/perf_counter.c
+++ b/arch/powerpc/kernel/perf_counter.c
@@ -534,7 +534,7 @@ void hw_perf_enable(void)
                         continue;
                 }
                 val = 0;
-                if (counter->hw_event.irq_period) {
+                if (counter->hw.irq_period) {
                         left = atomic64_read(&counter->hw.period_left);
                         if (left < 0x80000000L)
                                 val = 0x80000000L - left;
@@ -829,8 +829,6 @@ const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
 
         if (!ppmu)
                 return ERR_PTR(-ENXIO);
-        if ((s64)counter->hw_event.irq_period < 0)
-                return ERR_PTR(-EINVAL);
         if (!perf_event_raw(&counter->hw_event)) {
                 ev = perf_event_id(&counter->hw_event);
                 if (ev >= ppmu->n_generic || ppmu->generic_events[ev] == 0)
@@ -901,7 +899,7 @@ const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
 
         counter->hw.config = events[n];
         counter->hw.counter_base = cflags[n];
-        atomic64_set(&counter->hw.period_left, counter->hw_event.irq_period);
+        atomic64_set(&counter->hw.period_left, counter->hw.irq_period);
 
         /*
          * See if we need to reserve the PMU.
@@ -934,6 +932,7 @@ const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
 static void record_and_restart(struct perf_counter *counter, long val,
                                struct pt_regs *regs, int nmi)
 {
+        u64 period = counter->hw.irq_period;
         s64 prev, delta, left;
         int record = 0;
 
@@ -948,11 +947,11 @@ static void record_and_restart(struct perf_counter *counter, long val,
          */
         val = 0;
         left = atomic64_read(&counter->hw.period_left) - delta;
-        if (counter->hw_event.irq_period) {
+        if (period) {
                 if (left <= 0) {
-                        left += counter->hw_event.irq_period;
+                        left += period;
                         if (left <= 0)
-                                left = counter->hw_event.irq_period;
+                                left = period;
                         record = 1;
                 }
                 if (left < 0x80000000L)
diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 5a7f718eb1e1..886dcf334bc3 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -286,11 +286,8 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
                 hwc->nmi = 1;
         }
 
-        hwc->irq_period = hw_event->irq_period;
-        if ((s64)hwc->irq_period <= 0 || hwc->irq_period > x86_pmu.max_period)
-                hwc->irq_period = x86_pmu.max_period;
-
-        atomic64_set(&hwc->period_left, hwc->irq_period);
+        atomic64_set(&hwc->period_left,
+                        min(x86_pmu.max_period, hwc->irq_period));
 
         /*
          * Raw event type provide the config in the event structure
@@ -458,7 +455,7 @@ x86_perf_counter_set_period(struct perf_counter *counter,
                              struct hw_perf_counter *hwc, int idx)
 {
         s64 left = atomic64_read(&hwc->period_left);
-        s64 period = hwc->irq_period;
+        s64 period = min(x86_pmu.max_period, hwc->irq_period);
         int err;
 
         /*