Re: thermald for OpenBMC

[Patrick Williams <patrick@stwcx.xyz>]

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Patrick,

On Mon, Apr 17, 2017 at 01:21:29PM -0700, Patrick Venture wrote:
> I'm working on a thermal control loop that'll operate within the openbmc
> framework(s) and wanted to provide a somewhat high level overview for
> thoughts.

We should connect you with Matt Spinler (mspinler) and Matt Barth
(msbarth) on IRC.  They have been working on implementing the "IBM fan
control algorithm" but I suspect there is a significant amount of
overlap.  Our intention was that you'd be able to reuse our
implementation and insert a different (low-level detailed) algorithm.

> The general design is to have a daemon that reads fans and temperatures
> from dbus (reaching out to phosphor-hwmon) as well as being able to receive
> temperatures and other sensor information over an OEM IPMI command.

Sounds good.  This is how it is suppose to work.

For the IPMI commands, the expectation would be that either the IPMI
provider or an application fed by the IPMI provider for these OEM
commands would implement the same xyz.openbmc_project.Sensor.Value
interface as the phosphor-hwmon.  This way the thermal algorithm really
doesn't need to know where the data comes from.

> The system will support zones defined (yes, probably in YAML).  A zone will
> have at least one exclusion fan, and at least one thermal sensor.  The
> thermal sensor can be shared.  There will be defaults provided in this
> configuration to act as fallbacks.

There is some code available to define zones via YAML.  Matt Spinler can
point you at these.

> The thermal loop will be margin based and attempt to drive the fans to
> maintain the temperature within operating temperature of the zones.  Each
> zone will be independently managed.

These sounds very similar to what their intended design is as well.  For
a zone there is a lower-threshold and an upper-threshold.  When the
temperature is above the upper-threshold, the fan speed is increased and
the fans are decreased when the temperature is below the
lower-threshold.  Again, the Matts can give you details on what the "IBM
fan control algorithm" design is.

> Because not all thermal sensors can necessarily be ready by the BMC, we
> need a method of getting that information from the host.  From a previous
> project, we have the notion of sending thermal margins for slow and quick
> (heat change) devices to a controller.

Is this the Host->BMC via IPMI you mentioned earlier or does the BMC
need to actively query the host in some cases?  Hopefully it is always
one direction.

-- 
Patrick Williams

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