From 7708d5f04de4dd5d2110df3244372b1e3f61bc7c Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 21 Apr 2017 12:52:52 +0200 Subject: sched/clock: Print a warning recommending 'tsc=unstable' With our switch to stable delayed until late_initcall(), the most likely cause of hitting mark_tsc_unstable() is the watchdog. The watchdog typically only triggers when creative BIOS'es fiddle with the TSC to hide SMI latency. Since the watchdog can only detect TSC fiddling after the fact all TSC clocks (including userspace GTOD) can already have reported funny values. The only way to fully avoid this, is manually marking the TSC unstable at boot. Suggest people do this on their broken systems. Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- kernel/sched/clock.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/sched/clock.c') diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index a2f847c6ada8..1a0d389d2f2b 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -175,6 +175,7 @@ static void __sched_clock_work(struct work_struct *work) for_each_possible_cpu(cpu) per_cpu(sched_clock_data, cpu) = *scd; + printk(KERN_WARNING "TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.\n"); printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n", scd->tick_gtod, __gtod_offset, scd->tick_raw, __sched_clock_offset); -- cgit v1.2.3-55-g7522