Synopsys DesignWare Cores (DWC) PCIe Performance Monitoring Unit (PMU)

DesignWare Cores (DWC) PCIe PMU

The PMU is a PCIe configuration space register block provided by each PCIe Root Port in a Vendor-Specific Extended Capability named RAS D.E.S (Debug, Error injection, and Statistics).

As the name indicates, the RAS DES capability supports system level debugging, AER error injection, and collection of statistics. To facilitate collection of statistics, Synopsys DesignWare Cores PCIe controller provides the following two features:

  • one 64-bit counter for Time Based Analysis (RX/TX data throughput and time spent in each low-power LTSSM state) and

  • one 32-bit counter for Event Counting (error and non-error events for a specified lane)

Note: There is no interrupt for counter overflow.

Time Based Analysis

Using this feature you can obtain information regarding RX/TX data throughput and time spent in each low-power LTSSM state by the controller. The PMU measures data in two categories:

  • Group#0: Percentage of time the controller stays in LTSSM states.

  • Group#1: Amount of data processed (Units of 16 bytes).

Lane Event counters

Using this feature you can obtain Error and Non-Error information in specific lane by the controller. The PMU event is selected by all of:

  • Group i

  • Event j within the Group i

  • Lane k

Some of the events only exist for specific configurations.

DesignWare Cores (DWC) PCIe PMU Driver

This driver adds PMU devices for each PCIe Root Port named based on the BDF of the Root Port. For example,

30:03.0 PCI bridge: Device 1ded:8000 (rev 01)

the PMU device name for this Root Port is dwc_rootport_3018.

The DWC PCIe PMU driver registers a perf PMU driver, which provides description of available events and configuration options in sysfs, see /sys/bus/event_source/devices/dwc_rootport_{bdf}.

The “format” directory describes format of the config fields of the perf_event_attr structure. The “events” directory provides configuration templates for all documented events. For example, “Rx_PCIe_TLP_Data_Payload” is an equivalent of “eventid=0x22,type=0x1”.

The “perf list” command shall list the available events from sysfs, e.g.:

$# perf list | grep dwc_rootport
dwc_rootport_3018/Rx_PCIe_TLP_Data_Payload/        [Kernel PMU event]
dwc_rootport_3018/rx_memory_read,lane=?/               [Kernel PMU event]

Time Based Analysis Event Usage

Example usage of counting PCIe RX TLP data payload (Units of bytes):

$# perf stat -a -e dwc_rootport_3018/Rx_PCIe_TLP_Data_Payload/

The average RX/TX bandwidth can be calculated using the following formula:

PCIe RX Bandwidth = Rx_PCIe_TLP_Data_Payload / Measure_Time_Window PCIe TX Bandwidth = Tx_PCIe_TLP_Data_Payload / Measure_Time_Window

Lane Event Usage

Each lane has the same event set and to avoid generating a list of hundreds of events, the user need to specify the lane ID explicitly, e.g.:

$# perf stat -a -e dwc_rootport_3018/rx_memory_read,lane=4/

The driver does not support sampling, therefore “perf record” will not work. Per-task (without “-a”) perf sessions are not supported.