linux-kernel - RE: tsc reliability for Intel Core 2 Duo "Conroe"

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Message-ID: <04f8be9a-78ea-45fc-9a6f-c788ca10ea69@default>
Date:	Thu, 27 May 2010 09:26:13 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	dan.magenheimer@...cle.com, Venkatesh Pallipadi <venki@...gle.com>,
	Len Brown <lenb@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: RE: tsc reliability for Intel Core 2 Duo "Conroe"

> After digging deeper, it appears that this processor is entering
> C2 (as can be seen /sys/devices/system/cpu/cpu*/cpuidle/ output below)
> despite the documentation I have, as well as this posting from Len:
> http://forum.soft32.com/linux/ACPI-states-Conroe-ftopict339089.html
> I wonder if C1E state is somehow incorrectly getting recorded as
> C2 state?  Or maybe TSC doesn't stop in C2 (TSC is most certainly
> not stopping), in which case the test in tsc_check_state() should
> be againt ACPI_STATE_C2?
> 
> In any case, this appears to now be an ACPI C-state question
> so thanks, Venki, for cc'ing Len... and tglx is off the hook :-)
> 
> Len, note that this box is an Intel SDP so if it is an odd
> duck, please just let me know... though I think I may have
> some Xen code to fix depending on the answer to the above.

Never mind... it appears this box has a BIOS setting to enable/disable
C2 that I didn't find in the documentation.  With C2 disabled,
TSC is properly selected as the clocksource.

Sorry for the noise.
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