linux-kernel - Re: Fw: [BUG 2.6.21-rc7] acpi_pm clocksource loses time on x86-64

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Message-Id: <200705090911.l499BHJL016845@harpo.it.uu.se>
Date:	Wed, 9 May 2007 11:11:17 +0200 (MEST)
From:	Mikael Pettersson <mikpe@...uu.se>
To:	lenb@...nel.org, mikpe@...uu.se
Cc:	ak@...e.de, johnstul@...ibm.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de
Subject: Re: Fw: [BUG 2.6.21-rc7] acpi_pm clocksource loses time on x86-64

On Tue, 8 May 2007 15:14:36 -0400, Len Brown wrote:
> On Friday 04 May 2007 03:42, Mikael Pettersson wrote:
> > On Thu, 03 May 2007 19:38:50 -0700, john stultz wrote:
> > > > 	So that slow acpi_pm on x86_64 seems to be connected w/ the idle loop.
> > > > I'm guessing the chipset halts the ACPI PM in lower C states. Do you
> > > > have any guesses as to what might differ between x86_64 and i386 ACPI
> > > > idle loops? Or might this be something different in what the BIOS
> > > > exports in x86_64 mode or i386 mode?
> > > 
> > > Mikael,
> > > 	Just trying to dig a bit more through the acpi_processor_idle code.
> > > Could you run "cat /proc/acpi/processor/CPU1/power" and reply w/ the
> > > output?
> > 
> > Here's that file with the x86-64 kernel:
> > 
> > active state:            C2
> > max_cstate:              C8
> > bus master activity:     00000000
> > maximum allowed latency: 20000 usec
> > states:
> >     C1:                  type[C1] promotion[C2] demotion[--] latency[000] usage[00107840] duration[00000000000000000000]
> >    *C2:                  type[C2] promotion[--] demotion[C1] latency[010] usage[-1987043693] duration[00000000003044809185]
> 
> it may be that the problem is C2, not C1 on this box and thus "idle=poll" may be
> overkill to workaround it.
> 
> You can disable C2 with "processor.max_cstate=1"
> 
> still a mystery, though, why this is different on i386 vs x86_64.
> what is in this file when booted in i386 mode?

With the i386 kernel it's as follows:

active state:            C2
max_cstate:              C8
bus master activity:     00000000
maximum allowed latency: 20000 usec
states:
    C1:                  type[C1] promotion[C2] demotion[--] latency[000] usage[00004550] duration[00000000000000000000]
   *C2:                  type[C2] promotion[--] demotion[C1] latency[010] usage[00813483] duration[00000000023188005661]

/Mikael
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