Commit 7708d5f0 authored Apr 21, 2017 by Peter Zijlstra Committed by Ingo Molnar May 15, 2017

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) <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>

parent 2e44b7dd

kernel/sched/clock.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -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);

Admin message