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authorPeter Zijlstra <peterz@infradead.org>2017-04-21 12:14:13 +0200
committerIngo Molnar <mingo@kernel.org>2017-05-15 10:15:18 +0200
commitb421b22b00b0011f6a2ce3561176c4e79e640c49 (patch)
tree26fa2e2baa7f403f66292a5f1e8b55ea0ceecf1f /arch/x86/kernel/tsc.c
parentcf15ca8deda86b27b66e27848b4b0fe58098fc0b (diff)
x86/tsc, sched/clock, clocksource: Use clocksource watchdog to provide stable sync points
Currently we keep sched_clock_tick() active for stable TSC in order to keep the per-CPU state semi up-to-date. The (obvious) problem is that by the time we detect TSC is borked, our per-CPU state is also borked. So hook into the clocksource watchdog and call a method after we've found it to still be stable. There's the obvious race where the TSC goes wonky between finding it stable and us running the callback, but closing that is too much work and not really worth it, since we're already detecting TSC wobbles after the fact, so we cannot, per definition, fully avoid funny clock values. And since the watchdog runs less often than the tick, this is also an optimization. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/tsc.c')
-rw-r--r--arch/x86/kernel/tsc.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 66015195bd18..c1b16b328abe 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1033,6 +1033,15 @@ static void tsc_cs_mark_unstable(struct clocksource *cs)
pr_info("Marking TSC unstable due to clocksource watchdog\n");
}
+static void tsc_cs_tick_stable(struct clocksource *cs)
+{
+ if (tsc_unstable)
+ return;
+
+ if (using_native_sched_clock())
+ sched_clock_tick_stable();
+}
+
/*
* .mask MUST be CLOCKSOURCE_MASK(64). See comment above read_tsc()
*/
@@ -1046,6 +1055,7 @@ static struct clocksource clocksource_tsc = {
.archdata = { .vclock_mode = VCLOCK_TSC },
.resume = tsc_resume,
.mark_unstable = tsc_cs_mark_unstable,
+ .tick_stable = tsc_cs_tick_stable,
};
void mark_tsc_unstable(char *reason)