Re: [External] RE: [PATCH v2] platform/x86: thinkpad_acpi: performance mode interface

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On 8/21/2020 4:00 PM, Limonciello, Mario wrote:
<snip>
+ +The sysfs entry provides the ability to return the current
status and to set
the +desired mode. For example:: + +        echo H >
/sys/devices/platform/thinkpad_acpi/dytc_perfmode +        echo
M > /sys/devices/platform/thinkpad_acpi/dytc_perfmode +
echo L > /sys/devices/platform/thinkpad_acpi/dytc_perfmode +

I was thinking about this some more, do you actually want another
mode that "disables"
this feature?   IE "O" turns it off an calls DYTC_DISABLE_CQL.

For example if a user wanted to test the recently landed code in
thermald 2.3
and compare performance between the two it seems like this and
that "might" fight.
As an outsider looking in - I of course may be wrong too here.

If at some point in the future thermald does a better job than
this implementation you
might also want an "out" to let thermald or another piece of
userland turn this off if it's in the picture.

I'm still digging into this one. Right now I haven't found a good
clean way of just disabling the firmware. Currently when thermald
goes in and tweaks the CPU power registers it has the effect of
overriding the FW anyway - but I appreciate that's not quite the
same as actually doing it explicitly.


What about a modprobe parameter to disable at least?  That would at
least make it pretty easy to make a change, reboot and compare with
thermald (or other software) without disabling the rest of the
functionality of the thinkpad_acpi driver.

The problem is I don't have a good way to disable the firmware (that I know of yet) so a modprobe parameter wouldn't really do much. I guess it could skip providing the sysfs entry points - but the FW will still be there doing it's thing, so I'm not sure I see the benefit of that. At least the sysfs entry point gives a bit more insight into what is going on.
Let me know if I'm missing something obvious.

Mark


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