[RESEND 2] [PATCH 0/2] Rewrite power limit notification interrupt handling

[RESEND 2] [PATCH 0/2] Rewrite power limit notification interrupt handling

[Len Brown]

[Excluse duplicates -- for some reason these didn't hit list archives or patchwork]


The "Power Limit Notification" (X86_FEATURE_PLN) was added in Sandy Bridge
to give the OS the option of knowing when the package has reached
a configured power threshold.

Linux-2.6.36 enabled this feature:
0199114c31798af5b83841b21759b64171060d9b
(x86, hwmon: Package Level Thermal/Power: power limit)

It enabld the interrupt, and the interrupt hander
added to the MCE log and printed to the console:

printk(KERN_CRIT "CPU%d: %s power limit notification (total events = %lu)
printk(KERN_INFO "CPU%d: %s power limit normal\n"

However, these events are quite routine on some systems under some conditions,
alarming customers and provoking un-necessary customer support calls.

So the MCE log entry was deleted in Linux-3.3:

29e9bf1841e4f9df13b4992a716fece7087dd237
(x86, mce, therm_throt: Don't report power limit and package level thermal throttle events in mcelog)

Here we delete the corresponding kernel console messages,
and then we disable the interrupt by default -- allowing it
to be enabled by cmdline for diagnosis purposes.

https://bugzilla.kernel.org/show_bug.cgi?id=36182

This pair of patches applies cleanly back to Linux-3.3.

Documentation/kernel-parameters.txt      |  2 ++
arch/x86/kernel/cpu/mcheck/therm_throt.c | 43 ++++++++++++++++++++++++++-----------------
 2 files changed, 28 insertions(+), 17 deletions(-)

This pair of patches applies cleanly back to Linux-3.3.

Fenghua Yu (2):
	[1/2] x86 thermal: Delete power-limit-notification console messages
	[2/2] x86 thermal: Disable power limit notification interrupt by default

Re: [RESEND 2] [PATCH 0/2] Rewrite power limit notification interrupt handling

[Prarit Bhargava]

Len,

>The "Power Limit Notification" (X86_FEATURE_PLN) was added in Sandy Bridge
>to give the OS the option of knowing when the package has reached
>a configured power threshold.

>printk(KERN_CRIT "CPU%d: %s power limit notification (total events = %lu)
>printk(KERN_INFO "CPU%d: %s power limit normal\n"

I'm seeing this on a widening number of systems, mostly newer Intel systems.

>However, these events are quite routine on some systems under some conditions,
>alarming customers and provoking un-necessary customer support calls.

The idea that these are "routine" just doesn't make sense to me.  Either this
warning is firing for a valid reason or it isn't.  If it isn't then the question
remains -- why is it firing?  Is it because of buggy FW or is something
actually wrong with the hardware?

P.