queue-4.4/sparc-perf-fix-updated-event-period-in-response-to-p.patch

   1 From 7524e06e17196bf3645819d600dc19f17514e3af Mon Sep 17 00:00:00 2001
   2 From: Young Xiao <92siuyang@gmail.com>
   3 Date: Wed, 29 May 2019 10:21:48 +0800
   4 Subject: sparc: perf: fix updated event period in response to
   5  PERF_EVENT_IOC_PERIOD
   6
   7 [ Upstream commit 56cd0aefa475079e9613085b14a0f05037518fed ]
   8
   9 The PERF_EVENT_IOC_PERIOD ioctl command can be used to change the
  10 sample period of a running perf_event. Consequently, when calculating
  11 the next event period, the new period will only be considered after the
  12 previous one has overflowed.
  13
  14 This patch changes the calculation of the remaining event ticks so that
  15 they are offset if the period has changed.
  16
  17 See commit 3581fe0ef37c ("ARM: 7556/1: perf: fix updated event period in
  18 response to PERF_EVENT_IOC_PERIOD") for details.
  19
  20 Signed-off-by: Young Xiao <92siuyang@gmail.com>
  21 Signed-off-by: David S. Miller <davem@davemloft.net>
  22 Signed-off-by: Sasha Levin <sashal@kernel.org>
  23 ---
  24  arch/sparc/kernel/perf_event.c | 4 ++++
  25  1 file changed, 4 insertions(+)
  26
  27 diff --git a/arch/sparc/kernel/perf_event.c b/arch/sparc/kernel/perf_event.c
  28 index a5d0c2f08110..815352d501f0 100644
  29 --- a/arch/sparc/kernel/perf_event.c
  30 +++ b/arch/sparc/kernel/perf_event.c
  31 @@ -889,6 +889,10 @@ static int sparc_perf_event_set_period(struct perf_event *event,
  32         s64 period = hwc->sample_period;
  33         int ret = 0;
  34
  35 +       /* The period may have been changed by PERF_EVENT_IOC_PERIOD */
  36 +       if (unlikely(period != hwc->last_period))
  37 +               left = period - (hwc->last_period - left);
  38 +
  39         if (unlikely(left <= -period)) {
  40                 left = period;
  41                 local64_set(&hwc->period_left, left);
  42 --
  43 2.20.1
  44