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

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Date:	Wed, 22 Jan 2014 13:30:22 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>
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 Wed, Jan 22, 2014 at 01:26:09PM +0100, Markus Trippelsdorf wrote:
> On 2014.01.22 at 13:07 +0100, Peter Zijlstra wrote:
> > On Wed, Jan 22, 2014 at 01:00:48PM +0100, Markus Trippelsdorf wrote:
> > > FYI it happens on real hardware on my machine:
> > > ...
> > > [    0.000000] Hierarchical RCU implementation.
> > > [    0.000000] NR_IRQS:4352 nr_irqs:712 16
> > > [    0.000000] spurious 8259A interrupt: IRQ7.
> > > [    0.000000] Console: colour VGA+ 80x25
> > > [    0.000000] console [tty0] enabled
> > > [    0.000000] hpet clockevent registered
> > > [    0.000000] tsc: Fast TSC calibration using PIT
> > > [    0.003333] tsc: Detected 3210.681 MHz processor
> > > [   60.375238] Calibrating delay loop (skipped), value calculated using timer frequency.. 6423.91 BogoMIPS (lpj=10702270)
> > > [   60.375240] pid_max: default: 32768 minimum: 301
> > > [   60.375259] Mount-cache hash table entries: 256
> > > [   60.375373] tseg: 0000000000
> > > [   60.375377] CPU: Physical Processor ID: 0
> > > [   60.375377] CPU: Processor Core ID: 0
> > > [   60.375378] mce: CPU supports 6 MCE banks
> > > [   60.375382] LVT offset 0 assigned for vector 0xf9
> > > [   60.375384] process: using AMD E400 aware idle routine
> > > [   60.375386] Last level iTLB entries: 4KB 512, 2MB 16, 4MB 8
> > 
> > Should have always happened like that I think. From the log it looks
> > like the moment we switch from jiffies to actual TSC in
> > arch/x86/kernel/tsc.c:sched_clock().
> > 
> > I don't think I changed the logic there, just switched from a condition
> > to a jump_label.
> 
> Well, v3.13 was fine. So it's definitely a regression. But it may be
> another issue. I will try to bisect later.

OK, weird, I'll see if I can spot anything.
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