linux-kernel - Re: [bisected] Clocksource tsc unstable git

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Date:	Fri, 29 Oct 2010 13:34:33 +0200
From:	Markus Trippelsdorf <markus@...ppelsdorf.de>
To:	Borislav Petkov <bp@...64.org>
Cc:	Borislav Petkov <bp@...en8.de>, john stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hpa@...ux.intel.com" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	"Herrmann3, Andreas" <Andreas.Herrmann3@....com>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"avi@...hat.com" <avi@...hat.com>,
	"mtosatti@...hat.com" <mtosatti@...hat.com>
Subject: Re: [bisected] Clocksource tsc unstable git

On Fri, Oct 29, 2010 at 12:27:13PM +0200, Borislav Petkov wrote:
> On Fri, Oct 29, 2010 at 04:30:13AM -0400, Markus Trippelsdorf wrote:
> > > Well, what do you know, the temporary "slowdown" triggered on my setup
> > > too. After waiting a minute maybe, the machine recovered and guess what
> > > appeared in dmesg:
> > > 
> > > [44729.650859] Clocksource tsc unstable (delta = -8615263009 ns)
> > > [44729.656229] Switching to clocksource hpet
> > > 
> > > I've reverted the changeset above and will run without it to check
> > > whether it makes any difference.
> > 
> > After further testing I've found out that the tsc- and the kvm-issue are
> > unrelated. IOW I get these "slowdowns" even with 34f971f6f7988be4
> > reverted.
> 
> hmm, I'll run with 34f971f6f798 reverted for a while just to confirm
> your observations...
> 
> > I guess John was right when he wrote:
> > > From your dmesg, I'd guess the hpet is the watchdog clocksource, so I
> > > be on the lookout for hpet related changes.
> > >
> > > Maybe does reverting 995bd3bb5c78f3ff71339803c0b8337ed36d64fb hide the
> > > issue?  
> > 
> > Because with 995bd3bb5c78f reverted I never had a single "slowdown" here.
> 
> That's strange, when we tested this one everything seemed fine so I
> guess this is one of those bugs which appear later, just as if out of
> nowhere.
> 
> Thomas, could it be that SMI fires in between the HPET write and
> subsequent read:
> 
> 	hpet_writel(cnt, HPET_Tn_CMP(timer));
> 
> 	...
> 
> 	res = (s32)(cnt - hpet_readl(HPET_COUNTER));
> 
> causing the -ETIME and thus a wait for HPET wraparound? My machine at
> least does SMI-initiated C1E so it could very well be the problem.
> 
> Markus, can you verify this on your system by compiling x86info from
> git://git.choralone.org/git/x86info and doing
> 
> ./lsmsr Int


x86info v1.28beta.  Dave Jones 2001-2010
Feedback to <davej@...hat.com>.

Found 4 CPUs
--------------------------------------------------------------------------
CPU #1
EFamily: 1 EModel: 0 Family: 15 Model: 4 Stepping: 2
CPU Model: Quad-Core Opteron/Phenom II (RB-C2)
Processor name string: AMD Phenom(tm) II X4 955 Processor
Monitor/Mwait: min/max line size 64/64, ecx bit 0 support, enumeration extension
SVM: revision 1, 64 ASIDs, np, lbrVirt, SVMLock, NRIPSave
Address Size: 48 bits virtual, 48 bits physical
The physical package has 4 of 4 possible cores implemented.
--------------------------------------------------------------------------
CPU #2
EFamily: 1 EModel: 0 Family: 15 Model: 4 Stepping: 2
CPU Model: Quad-Core Opteron/Phenom II (RB-C2)
Processor name string: AMD Phenom(tm) II X4 955 Processor
Monitor/Mwait: min/max line size 64/64, ecx bit 0 support, enumeration extension
SVM: revision 1, 64 ASIDs, np, lbrVirt, SVMLock, NRIPSave
Address Size: 48 bits virtual, 48 bits physical
The physical package has 4 of 4 possible cores implemented.
--------------------------------------------------------------------------
CPU #3
EFamily: 1 EModel: 0 Family: 15 Model: 4 Stepping: 2
CPU Model: Quad-Core Opteron/Phenom II (RB-C2)
Processor name string: AMD Phenom(tm) II X4 955 Processor
Monitor/Mwait: min/max line size 64/64, ecx bit 0 support, enumeration extension
SVM: revision 1, 64 ASIDs, np, lbrVirt, SVMLock, NRIPSave
Address Size: 48 bits virtual, 48 bits physical
The physical package has 4 of 4 possible cores implemented.
--------------------------------------------------------------------------
CPU #4
EFamily: 1 EModel: 0 Family: 15 Model: 4 Stepping: 2
CPU Model: Quad-Core Opteron/Phenom II (RB-C2)
Processor name string: AMD Phenom(tm) II X4 955 Processor
Monitor/Mwait: min/max line size 64/64, ecx bit 0 support, enumeration extension
SVM: revision 1, 64 ASIDs, np, lbrVirt, SVMLock, NRIPSave
Address Size: 48 bits virtual, 48 bits physical
The physical package has 4 of 4 possible cores implemented.
--------------------------------------------------------------------------
 running at an estimated 3.20GHz

x86info --all output is attached
-- 
Markus

View attachment "x86info_all" of type "text/plain" (35073 bytes)