target/linux/pistachio/patches-4.14/107-clockevents-Retry-programming-min-delta-up-to-10-tim.patch

   1 From b46f8c74afdd30cd52bfdcc2231470a0bab04416 Mon Sep 17 00:00:00 2001
   2 From: James Hogan <james.hogan@imgtec.com>
   3 Date: Fri, 22 Apr 2016 18:22:45 +0100
   4 Subject: clockevents: Retry programming min delta up to 10 times
   5
   6 Under virtualisation it is possible to get unexpected latency during a
   7 clockevent device's set_next_event() callback which can make it return
   8 -ETIME even for a delta based on min_delta_ns.
   9
  10 The clockevents_program_min_delta() implementation for
  11 CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST=n doesn't handle retries when this
  12 happens, nor does clockevents_program_event() or its callers when force
  13 is true (for example hrtimer_reprogram()). This can result in hangs
  14 until the clock event device does a full period.
  15
  16 It isn't appropriate to use MIN_ADJUST in this case as occasional
  17 hypervisor induced high latency will cause min_delta_ns to quickly
  18 increase to the maximum.
  19 Instead, borrow the retry pattern from the MIN_ADJUST case, but without
  20 making adjustments. We retry up to 10 times before giving up.
  21
  22 (picked https://patchwork.kernel.org/patch/8909491/)
  23
  24 Signed-off-by: James Hogan <james.hogan@imgtec.com>
  25 ---
  26  kernel/time/clockevents.c | 26 +++++++++++++++++++-------
  27  1 file changed, 19 insertions(+), 7 deletions(-)
  28
  29 --- a/kernel/time/clockevents.c
  30 +++ b/kernel/time/clockevents.c
  31 @@ -281,16 +281,28 @@ static int clockevents_program_min_delta
  32  {
  33         unsigned long long clc;
  34         int64_t delta;
  35 +       int i;
  36
  37 -       delta = dev->min_delta_ns;
  38 -       dev->next_event = ktime_add_ns(ktime_get(), delta);
  39 +       for (i = 0;;) {
  40 +               delta = dev->min_delta_ns;
  41 +               dev->next_event = ktime_add_ns(ktime_get(), delta);
  42
  43 -       if (clockevent_state_shutdown(dev))
  44 -               return 0;
  45 +               if (clockevent_state_shutdown(dev))
  46 +                       return 0;
  47
  48 -       dev->retries++;
  49 -       clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
  50 -       return dev->set_next_event((unsigned long) clc, dev);
  51 +               dev->retries++;
  52 +               clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
  53 +               if (dev->set_next_event((unsigned long) clc, dev) == 0)
  54 +                       return 0;
  55 +
  56 +               if (++i > 9) {
  57 +                       /*
  58 +                        * We tried 10 times to program the device with the
  59 +                        * given min_delta_ns. Get out of here.
  60 +                        */
  61 +                       return -ETIME;
  62 +               }
  63 +       }
  64  }
  65
  66  #endif /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */