[patch] Re: x86-tip tsc/tick gripage

[Mike Galbraith <efault@gmx.de>]

On Wed, 2017-04-26 at 13:39 +0200, Mike Galbraith wrote:
> On Wed, 2017-04-26 at 12:26 +0200, Peter Zijlstra wrote:
> > On Wed, Apr 26, 2017 at 10:57:42AM +0200, Mike Galbraith wrote:
> > 
> > > Both still lose their TSC.
> > > 
> > > [   11.982468] tsc: Refined TSC clocksource calibration: 2260.999 MHz
> > > [   11.994275] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x20974a4d8bb, max_idle_ns: 440795246623 ns
> > > [   13.064172] clocksource: Switched to clocksource tsc
> > > [  240.247851] clocksource: timekeeping watchdog on CPU23: Marking clocksource 'tsc' as unstable because the skew is too large:
> > > [  240.462501] clocksource:                       'tsc' cs_now: 108fe5be09f cs_last: b90a6a0676 mask: ffffffffffffffff
> > > [  240.675057] tsc: Marking TSC unstable due to clocksource watchdog
> > 
> > 
> > And they didn't use to? We don't typically write to TSC or TSC_ADJUST
> > and thus would not cause such behaviour.
> 
> Nope.  The DL980 is my RT jitter test box, which I use all the time. 

I found evidence of lysdexia at play (hunk 2), below is an RFFS (frozen
shark) which makes my DL980 a happy camper with tip.

timer/nohz: Call tick_tmigr_idle() with proper parameter order

Extremely late timer expiration soon leads to the clocksource watchdog
killing the TSC clocksource on multisocket boxen.  Call tmigr_cpu_idle(
) with proper parameter order, and pass next_local to tmigr_cpu_idle()
so it can return what it says it returns.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Fixes: ec2206b91d43 timer: Implement the hierarchical pull model
---
 kernel/time/tick-sched.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -695,7 +695,7 @@ tick_tmigr_idle(struct tick_sched *ts, u
 	if (next_global >= next_local)
 		next_global = KTIME_MAX;
 
-	next_global = tmigr_cpu_idle(next_global);
+	next_local = tmigr_cpu_idle(next_local);
 
 	return min_t(u64, next_local, next_global);
 }
@@ -768,7 +768,7 @@ static ktime_t tick_nohz_stop_sched_tick
 	 */
 	delta = next_local - basemono;
 	if (delta > (u64)TICK_NSEC)
-		next_local = tick_tmigr_idle(ts, next_local, next_global);
+		next_local = tick_tmigr_idle(ts, next_global, next_local);
 
 	ts->next_timer = next_local;