When we have more than one CPU in system, counter synchronisation
overhead can lead to a scenario that sched_clock goes backward when
being read from different CPUs.
This is accommodated by CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, but it's
unavailable on 32bit kernel.
We don't want to risk sched_clock correctness, so if we have multiple
CPU in system and CONFIG_HAVE_UNSTABLE_SCHED_CLOCK is not set, we just
don't use counter as sched_clock source.
Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
---
arch/mips/kernel/csrc-r4k.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/arch/mips/kernel/csrc-r4k.c b/arch/mips/kernel/csrc-r4k.c
index 055747a7417d..bdb1fa8931f4 100644
--- a/arch/mips/kernel/csrc-r4k.c
+++ b/arch/mips/kernel/csrc-r4k.c
@@ -68,6 +68,18 @@ static bool rdhwr_count_usable(void)
return false;
}
+static inline __init bool count_can_be_sched_clock(void)
+{
+ if (IS_ENABLED(CONFIG_CPU_FREQ))
+ return false;
+
+ if (num_possible_cpus() > 1 &&
+ !IS_ENABLED(CONFIG_HAVE_UNSTABLE_SCHED_CLOCK))
+ return false;
+
+ return true;
+}
+
#ifdef CONFIG_CPU_FREQ
static bool __read_mostly r4k_clock_unstable;
@@ -125,9 +137,8 @@ int __init init_r4k_clocksource(void)
clocksource_register_hz(&clocksource_mips, mips_hpt_frequency);
-#ifndef CONFIG_CPU_FREQ
- sched_clock_register(r4k_read_sched_clock, 32, mips_hpt_frequency);
-#endif
+ if (count_can_be_sched_clock())
+ sched_clock_register(r4k_read_sched_clock, 32, mips_hpt_frequency);
return 0;
}
--
2.43.0
