Inconsistent performance of dbus call GetManagedObjects to PSUSensor in dbus-sensors

[Alex Qiu]

Hi folks,

I'm branching this topic as Jason mentioned about this in the other topic
that he started, and I'll report the information I have for now. Sui and
Jie will follow up on this as they are actively working on this issue.

The setup has a total of 249 IPMI sensors, and among these, dbus-sensors
reports 59 objects from HwmonTempSensor and 195 objects from PSUSensor, and
we've already decreased the polling rate of PSUSensor to every 10 seconds
to mitigate the issue. As the intel-ipmi-oem does, we measure the time of
calling GetManagedObjects with commands:

time busctl call xyz.openbmc_project.HwmonTempSensor /
org.freedesktop.DBus.ObjectManager GetManagedObjects
time busctl call xyz.openbmc_project.PSUSensor /
org.freedesktop.DBus.ObjectManager GetManagedObjects

The first command for HwmonTempSensor constantly finishes in about 60 ms.
However, the run time of the second command for PSUSensor is very
inconsistent. Out of 50 continuous runs, most of them finish in about 150
ms, but 2 or 3 of them will take as long as about 6 seconds to return. This
results in long time to scan the SDR and inconsistent performance polling
IPMI sensors.

Thanks.

- Alex Qiu
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