[PATCH AUTOSEL 4.14 15/27] sparc: perf: fix updated event period in response to PERF_EVENT_IOC_PERIOD

[Sasha Levin <sashal@kernel.org>]

From: Young Xiao <92siuyang@gmail.com>

[ Upstream commit 56cd0aefa475079e9613085b14a0f05037518fed ]

The PERF_EVENT_IOC_PERIOD ioctl command can be used to change the
sample period of a running perf_event. Consequently, when calculating
the next event period, the new period will only be considered after the
previous one has overflowed.

This patch changes the calculation of the remaining event ticks so that
they are offset if the period has changed.

See commit 3581fe0ef37c ("ARM: 7556/1: perf: fix updated event period in
response to PERF_EVENT_IOC_PERIOD") for details.

Signed-off-by: Young Xiao <92siuyang@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/sparc/kernel/perf_event.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/sparc/kernel/perf_event.c b/arch/sparc/kernel/perf_event.c
index eceb0215bdee..58ea64a29d5f 100644
--- a/arch/sparc/kernel/perf_event.c
+++ b/arch/sparc/kernel/perf_event.c
@@ -891,6 +891,10 @@ static int sparc_perf_event_set_period(struct perf_event *event,
 	s64 period = hwc->sample_period;
 	int ret = 0;
 
+	/* The period may have been changed by PERF_EVENT_IOC_PERIOD */
+	if (unlikely(period != hwc->last_period))
+		left = period - (hwc->last_period - left);
+
 	if (unlikely(left <= -period)) {
 		left = period;
 		local64_set(&hwc->period_left, left);
-- 
2.20.1