New AMD Dynamic EPP Feature Causing Some Problems With Linux 7.1
Dynamic EPP is one of the new AMD P-State features in Linux 7.1, but, unfortunately is causing some fallout in early usage of this power-savings related functionality.
Dynamic Energy Performance Preference (EPP) allows changing the performance profile depending upon whether the Ryzen laptop is running on AC or DC power. EPP values are dynamically adjusted based on the power state and adjust based on plug-in/out events as well as other contributing factors like the ACPI Platform Profile. The kernel is autonomously in control of setting the EPP mode and manual writes to the EPP interface for the AMD P-State driver are blocked.
It turns out though that there are some unexpected performance issues coming up from Dynamic EPP. This patch was posted for now dropping the Kconfig build option for allowing Dynamic EPP to be enabled by default. The patch message explains of some yet unresolved performance issues:
The amd_pstate.dynamic_epp=1 module parameter can be used for manually enabling Dynamic EPP if so desired.
This patch along with other Dynamic EPP related fixes were sent out today to the Linux power management subsystem's "fixes" for in turn getting into Linux 7.1 Git in the days ahead.
The other Dynamic EPP work includes some improved error handling, permitting writes to dynamic_epp when the state isn't modified, and other changes. Hopefully AMD Dynamic EPP will be in better shape for restoring the Kconfig default option by the time of the Linux v7.2 merge window next month.
Dynamic Energy Performance Preference (EPP) allows changing the performance profile depending upon whether the Ryzen laptop is running on AC or DC power. EPP values are dynamically adjusted based on the power state and adjust based on plug-in/out events as well as other contributing factors like the ACPI Platform Profile. The kernel is autonomously in control of setting the EPP mode and manual writes to the EPP interface for the AMD P-State driver are blocked.
It turns out though that there are some unexpected performance issues coming up from Dynamic EPP. This patch was posted for now dropping the Kconfig build option for allowing Dynamic EPP to be enabled by default. The patch message explains of some yet unresolved performance issues:
"There are some performance issues being identified by dynamic EPP and we don't want to have distributions turning it on by default exposing them to users at this time.
Drop the kconfig option, and require an explicit opt in from kernel command line or runtime sysfs option to turn it on."
The amd_pstate.dynamic_epp=1 module parameter can be used for manually enabling Dynamic EPP if so desired.
This patch along with other Dynamic EPP related fixes were sent out today to the Linux power management subsystem's "fixes" for in turn getting into Linux 7.1 Git in the days ahead.
The other Dynamic EPP work includes some improved error handling, permitting writes to dynamic_epp when the state isn't modified, and other changes. Hopefully AMD Dynamic EPP will be in better shape for restoring the Kconfig default option by the time of the Linux v7.2 merge window next month.