linux-kernel - Re: [PATCH 13/15] sched: Use a static_key for sched_clock

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Message-ID: <20140122190905.GA391@x4>
Date:	Wed, 22 Jan 2014 20:09:05 +0100
From:	Markus Trippelsdorf <markus@...ppelsdorf.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Arjan van de Ven <arjan@...ux.intel.com>, lenb@...nel.org,
	rjw@...ysocki.net, Eliezer Tamir <eliezer.tamir@...ux.intel.com>,
	rui.zhang@...el.com, jacob.jun.pan@...ux.intel.com,
	Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...nel.org>, hpa@...or.com,
	paulmck@...ux.vnet.ibm.com, Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>,
	Andy Lutomirski <luto@...capital.net>,
	linux-kernel@...r.kernel.org, dyoung@...hat.com
Subject: Re: [PATCH 13/15] sched: Use a static_key for sched_clock_stable

On 2014.01.22 at 19:42 +0100, Peter Zijlstra wrote:
> On Wed, Jan 22, 2014 at 07:35:38PM +0100, Markus Trippelsdorf wrote:
> 
> > >FYI it happens on real hardware on my machine:
> 
> > >[   60.375384] process: using AMD E400 aware idle routine
> 
> > But this is a different issue. I've bisected it to:
> > 
> > commit 20d1c86a57762f0a33a78988e3fc8818316badd4
> > Author: Peter Zijlstra <peterz@...radead.org>
> > Date:   Fri Nov 29 15:40:29 2013 +0100
> > 
> >     sched/clock, x86: Rewrite cyc2ns() to avoid the need to disable IRQs
> > 
> > Reverting the commit "fixes" the issue:
> 
> Hurm..

Turns out the fix is simple:

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index a3acbac2ee72..d90f7a11d573 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1198,8 +1198,8 @@ void __init tsc_init(void)
 	 * up if their speed diverges)
 	 */
 	for_each_possible_cpu(cpu) {
-		cyc2ns_init(cpu);
 		set_cyc2ns_scale(cpu_khz, cpu);
+		cyc2ns_init(cpu);
 	}
 
 	if (tsc_disabled > 0)

-- 
Markus
--
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