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

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Date:	Wed, 22 Jan 2014 14:17:58 -0500
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Len Brown <lenb@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Eliezer Tamir <eliezer.tamir@...ux.intel.com>,
	Zhang Rui <rui.zhang@...el.com>, jacob.jun.pan@...ux.intel.com,
	Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Paul McKenney <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" <linux-kernel@...r.kernel.org>,
	Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH 13/15] sched: Use a static_key for sched_clock_stable

On Wed, Jan 22, 2014 at 1:45 PM, Markus Trippelsdorf
<markus@...ppelsdorf.de> wrote:
> 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.. what kind of AMD machine is that?
>
> It's an ancient one:
>
> processor       : 0
> vendor_id       : AuthenticAMD
> cpu family      : 16
> model           : 4
> model name      : AMD Phenom(tm) II X4 955 Processor
> stepping        : 2
> microcode       : 0x10000db
> cpu MHz         : 800.000
> cache size      : 512 KB
> physical id     : 0
> siblings        : 4
> core id         : 0
> cpu cores       : 4
> apicid          : 0
> initial apicid  : 0
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 5
> wp              : yes
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm 3dnowext 3
> dnow constant_tsc rep_good nopl nonstop_tsc extd_apicid pni monitor cx16 popcnt lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit
> wdt hw_pstate npt lbrv svm_lock nrip_save
> bogomips        : 6424.73
> TLB size        : 1024 4K pages
> clflush size    : 64
> cache_alignment : 64
> address sizes   : 48 bits physical, 48 bits virtual
> power management: ts ttp tm stc 100mhzsteps hwpstate

I'm seeing the odd printk timestamp jump going from 0.xxx to 49.xx on
an i7-2600 so it isn't just old hardware.

[    0.000000] kmemleak: Kernel memory leak detector disabled
[    0.000000] ODEBUG: 32 of 32 active objects replaced
[    0.000000] hpet clockevent registered
[    0.000000] tsc: Fast TSC calibration using PIT
[    0.001000] tsc: Detected 3392.351 MHz processor
[   49.777360] Calibrating delay loop (skipped), value calculated
using timer frequency.. 6784.70 BogoMIPS (lpj=3392351)
[   49.777363] pid_max: default: 32768 minimum: 301
[   49.777572] Security Framework initialized


josh
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