From: Peter Zijlstra <peterz@infradead.org>
To: tglx@linutronix.de, mingo@kernel.org
Cc: linux-kernel@vger.kernel.org, ville.syrjala@linux.intel.com,
daniel.lezcano@linaro.org, rafael.j.wysocki@intel.com,
marta.lofstedt@intel.com, martin.peres@linux.intel.com,
pasha.tatashin@oracle.com, peterz@infradead.org,
daniel.vetter@ffwll.ch
Subject: [PATCH 9/9] sched/clock: Print a warning recommending tsc=unstable
Date: Fri, 21 Apr 2017 16:58:05 +0200 [thread overview]
Message-ID: <20170421150734.346212152@infradead.org> (raw)
In-Reply-To: 20170421145756.305735607@infradead.org
[-- Attachment #1: peterz-sched-clock-rubarb-10.patch --]
[-- Type: text/plain, Size: 1090 bytes --]
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>
---
kernel/sched/clock.c | 1 +
1 file changed, 1 insertion(+)
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -175,6 +175,7 @@ static void __sched_clock_work(struct wo
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);
next prev parent reply other threads:[~2017-04-21 17:08 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-21 14:57 [PATCH 0/9] sched_clock fixes Peter Zijlstra
2017-04-21 14:57 ` [PATCH 1/9] x86/tsc: Provide tsc=unstable boot parameter Peter Zijlstra
2017-04-21 14:57 ` [PATCH 2/9] x86,tsc: Feed refined TSC calibration into sched_clock Peter Zijlstra
2017-04-21 14:57 ` [PATCH 3/9] sched/clock: Initialize all per-cpu state before switching (back) to unstable Peter Zijlstra
2017-04-21 14:58 ` [PATCH 4/9] x86/tsc,sched/clock,clocksource: Use clocksource watchdog to provide stable sync points Peter Zijlstra
2017-04-21 14:58 ` [PATCH 5/9] sched/clock: Remove unused argument to sched_clock_idle_wakeup_event() Peter Zijlstra
2017-04-21 14:58 ` [PATCH 6/9] sched/clock: Remove watchdog touching Peter Zijlstra
2017-04-21 15:28 ` Peter Zijlstra
2017-04-21 14:58 ` [PATCH 8/9] sched/clock: Use late_initcall() instead of sched_init_smp() Peter Zijlstra
2017-04-21 14:58 ` Peter Zijlstra [this message]
2017-04-25 9:31 ` [PATCH 0/9] sched_clock fixes Lofstedt, Marta
2017-04-25 13:44 ` Peter Zijlstra
2017-04-26 6:41 ` Lofstedt, Marta
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