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>
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@ -175,6 +175,7 @@ static void __sched_clock_work(struct work_struct *work)
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for_each_possible_cpu(cpu)
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per_cpu(sched_clock_data, cpu) = *scd;
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printk(KERN_WARNING "TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.\n");
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printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n",
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scd->tick_gtod, __gtod_offset,
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scd->tick_raw, __sched_clock_offset);
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