[UNTESTED][PATCH] perf/x86: Fix limit_period() for 'freq mode events'

[Ravi Bangoria]

For the freq mode event ...

event->attr.sample_period contains sampling freq, not the sample period.
So, use actual sample period (event->hw.sample_period) while calling
limit_period().

Kernel dynamically adjusts event sample period after every sample to meet
the desire sampling freq. For this, kernel starts with sample period = 1
and gradually increase it. Instead of simply returning error, start
calibrating freq with the minimum sample period provided by limit_period().

Similarly, value provided along with ioctl(PERF_EVENT_IOC_PERIOD) contains
new freq not the sample period. Avoid calling limit_period() for freq mode
event in the ioctl() code path.

Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxx>
---
UNTESTED: limit_period() is mostly defined by Intel PMUs and I don't have
any of those test machines.

 arch/x86/events/core.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index c75c482d4c52..924aa35676d3 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -629,10 +629,22 @@ int x86_pmu_hw_config(struct perf_event *event)
 		event->hw.config |= x86_pmu_get_event_config(event);
 
 	if (event->attr.sample_period && x86_pmu.limit_period) {
-		s64 left = event->attr.sample_period;
-		x86_pmu.limit_period(event, &left);
-		if (left > event->attr.sample_period)
-			return -EINVAL;
+		if (event->attr.freq) {
+			s64 left = event->hw.sample_period;
+
+			x86_pmu.limit_period(event, &left);
+			if (left != event->hw.sample_period) {
+				event->hw.sample_period = left;
+				event->hw.last_period = left;
+				local64_set(&event->hw.period_left, left);
+			}
+		} else {
+			s64 left = event->attr.sample_period;
+
+			x86_pmu.limit_period(event, &left);
+			if (left > event->attr.sample_period)
+				return -EINVAL;
+		}
 	}
 
 	/* sample_regs_user never support XMM registers */
@@ -2648,6 +2660,9 @@ static int x86_pmu_check_period(struct perf_event *event, u64 value)
 	if (x86_pmu.check_period && x86_pmu.check_period(event, value))
 		return -EINVAL;
 
+	if (event->attr.freq)
+		return 0;
+
 	if (value && x86_pmu.limit_period) {
 		s64 left = value;
 		x86_pmu.limit_period(event, &left);
-- 
2.34.1