HiSilicon PCIe Tune and Trace device¶
HiSilicon PCIe tune and trace device (PTT) is a PCIe Root Complex integrated Endpoint (RCiEP) device, providing the capability to dynamically monitor and tune the PCIe link’s events (tune), and trace the TLP headers (trace). The two functions are independent, but is recommended to use them together to analyze and enhance the PCIe link’s performance.
On Kunpeng 930 SoC, the PCIe Root Complex is composed of several PCIe cores. Each PCIe core includes several Root Ports and a PTT RCiEP, like below. The PTT device is capable of tuning and tracing the links of the PCIe core.
+--------------Core 0-------+ | | [ PTT ] | | | [Root Port]---[Endpoint] | | [Root Port]---[Endpoint] | | [Root Port]---[Endpoint] Root Complex |------Core 1-------+ | | [ PTT ] | | | [Root Port]---[ Switch ]---[Endpoint] | | [Root Port]---[Endpoint] `-[Endpoint] | | [Root Port]---[Endpoint] +---------------------------+
The PTT device driver registers one PMU device for each PTT device. The name of each PTT device is composed of ‘hisi_ptt’ prefix with the id of the SICL and the Core where it locates. The Kunpeng 930 SoC encapsulates multiple CPU dies (SCCL, Super CPU Cluster) and IO dies (SICL, Super I/O Cluster), where there’s one PCIe Root Complex for each SICL.
PTT tune is designed for monitoring and adjusting PCIe link parameters (events). Currently we support events in 2 classes. The scope of the events covers the PCIe core to which the PTT device belongs.
Each event is presented as a file under $(PTT PMU dir)/tune, and a simple open/read/write/close cycle will be used to tune the event.
$ cd /sys/devices/hisi_ptt<sicl_id>_<core_id>/tune $ ls qos_tx_cpl qos_tx_np qos_tx_p tx_path_rx_req_alloc_buf_level tx_path_tx_req_alloc_buf_level $ cat qos_tx_dp 1 $ echo 2 > qos_tx_dp $ cat qos_tx_dp 2
Current value (numerical value) of the event can be simply read from the file, and the desired value written to the file to tune.
1. Tx Path QoS Control¶
The following files are provided to tune the QoS of the tx path of the PCIe core.
qos_tx_cpl: weight of Tx completion TLPs
qos_tx_np: weight of Tx non-posted TLPs
qos_tx_p: weight of Tx posted TLPs
The weight influences the proportion of certain packets on the PCIe link. For example, for the storage scenario, increase the proportion of the completion packets on the link to enhance the performance as more completions are consumed.
The available tune data of these events is [0, 1, 2]. Writing a negative value will return an error, and out of range values will be converted to 2. Note that the event value just indicates a probable level, but is not precise.
2. Tx Path Buffer Control¶
Following files are provided to tune the buffer of tx path of the PCIe core.
rx_alloc_buf_level: watermark of Rx requested
tx_alloc_buf_level: watermark of Tx requested
These events influence the watermark of the buffer allocated for each type. Rx means the inbound while Tx means outbound. The packets will be stored in the buffer first and then transmitted either when the watermark reached or when timed out. For a busy direction, you should increase the related buffer watermark to avoid frequently posting and thus enhance the performance. In most cases just keep the default value.
The available tune data of above events is [0, 1, 2]. Writing a negative value will return an error, and out of range values will be converted to 2. Note that the event value just indicates a probable level, but is not precise.
PTT trace is designed for dumping the TLP headers to the memory, which can be used to analyze the transactions and usage condition of the PCIe Link. You can choose to filter the traced headers by either Requester ID, or those downstream of a set of Root Ports on the same core of the PTT device. It’s also supported to trace the headers of certain type and of certain direction.
You can use the perf command perf record to set the parameters, start trace and get the data. It’s also supported to decode the trace data with perf report. The control parameters for trace is inputted as event code for each events, which will be further illustrated later. An example usage is like
$ perf record -e hisi_ptt0_2/filter=0x80001,type=1,direction=1, format=1/ -- sleep 5
This will trace the TLP headers downstream root port 0000:00:10.1 (event code for event ‘filter’ is 0x80001) with type of posted TLP requests, direction of inbound and traced data format of 8DW.
The TLP headers to trace can be filtered by the Root Ports or the Requester ID of the Endpoint, which are located on the same core of the PTT device. You can set the filter by specifying the filter parameter which is required to start the trace. The parameter value is 20 bit. Bit 19 indicates the filter type. 1 for Root Port filter and 0 for Requester filter. Bit[15:0] indicates the filter value. The value for a Root Port is a mask of the core port id which is calculated from its PCI Slot ID as (slotid & 7) * 2. The value for a Requester is the Requester ID (Device ID of the PCIe function). Bit[18:16] is currently reserved for extension.
For example, if the desired filter is Endpoint function 0000:01:00.1 the filter value will be 0x00101. If the desired filter is Root Port 0000:00:10.0 then then filter value is calculated as 0x80001.
Note that multiple Root Ports can be specified at one time, but only one Endpoint function can be specified in one trace. Specifying both Root Port and function at the same time is not supported. Driver maintains a list of available filters and will check the invalid inputs.
Currently the available filters are detected in driver’s probe. If the supported devices are removed/added after probe, you may need to reload the driver to update the filters.
You can trace the TLP headers of certain types by specifying the type parameter, which is required to start the trace. The parameter value is 8 bit. Current supported types and related values are shown below:
8’b00000001: posted requests (P)
8’b00000010: non-posted requests (NP)
8’b00000100: completions (CPL)
You can specify multiple types when tracing inbound TLP headers, but can only specify one when tracing outbound TLP headers.
You can trace the TLP headers from certain direction, which is relative to the Root Port or the PCIe core, by specifying the direction parameter. This is optional and the default parameter is inbound. The parameter value is 4 bit. When the desired format is 4DW, directions and related values supported are shown below:
4’b0000: inbound TLPs (P, NP, CPL)
4’b0001: outbound TLPs (P, NP, CPL)
4’b0010: outbound TLPs (P, NP, CPL) and inbound TLPs (P, NP, CPL B)
4’b0011: outbound TLPs (P, NP, CPL) and inbound TLPs (CPL A)
When the desired format is 8DW, directions and related values supported are shown below:
4’b0001: outbound TLPs (P, NP, CPL)
4’b0010: inbound TLPs (P, NP, CPL B)
4’b0011: inbound TLPs (CPL A)
Inbound completions are classified into two types:
completion A (CPL A): completion of CHI/DMA/Native non-posted requests, except for CPL B
completion B (CPL B): completion of DMA remote2local and P2P non-posted requests
You can change the format of the traced TLP headers by specifying the format parameter. The default format is 4DW. The parameter value is 4 bit. Current supported formats and related values are shown below:
4’b0000: 4DW length per TLP header
4’b0001: 8DW length per TLP header
The traced TLP header format is different from the PCIe standard.
When using the 8DW data format, the entire TLP header is logged (Header DW0-3 shown below). For example, the TLP header for Memory Reads with 64-bit addresses is shown in PCIe r5.0, Figure 2-17; the header for Configuration Requests is shown in Figure 2.20, etc.
In addition, 8DW trace buffer entries contain a timestamp and possibly a prefix for a PASID TLP prefix (see Figure 6-20, PCIe r5.0). Otherwise this field will be all 0.
The bit[31:11] of DW0 is always 0x1fffff, which can be used to distinguish the data format. 8DW format is like
bits [ 31:11 ][ 10:0 ] |---------------------------------------|-------------------| DW0 [ 0x1fffff ][ Reserved (0x7ff) ] DW1 [ Prefix ] DW2 [ Header DW0 ] DW3 [ Header DW1 ] DW4 [ Header DW2 ] DW5 [ Header DW3 ] DW6 [ Reserved (0x0) ] DW7 [ Time ]
When using the 4DW data format, DW0 of the trace buffer entry contains selected fields of DW0 of the TLP, together with a timestamp. DW1-DW3 of the trace buffer entry contain DW1-DW3 directly from the TLP header.
4DW format is like
bits [31:30] [ 29:25 ][ 20:11 ][ 10:0 ] |-----|---------|---|---|---|---|-------------|-------------| DW0 [ Fmt ][ Type ][T9][T8][TH][SO][ Length ][ Time ] DW1 [ Header DW1 ] DW2 [ Header DW2 ] DW3 [ Header DW3 ]
5. Memory Management¶
The traced TLP headers will be written to the memory allocated by the driver. The hardware accepts 4 DMA address with same size, and writes the buffer sequentially like below. If DMA addr 3 is finished and the trace is still on, it will return to addr 0.
+->[DMA addr 0]->[DMA addr 1]->[DMA addr 2]->[DMA addr 3]-+ +---------------------------------------------------------+
Driver will allocate each DMA buffer of 4MiB. The finished buffer will be copied to the perf AUX buffer allocated by the perf core. Once the AUX buffer is full while the trace is still on, driver will commit the AUX buffer first and then apply for a new one with the same size. The size of AUX buffer is default to 16MiB. User can adjust the size by specifying the -m parameter of the perf command.
You can decode the traced data with perf report -D command (currently only support to dump the raw trace data). The traced data will be decoded according to the format described previously (take 8DW as an example):
[...perf headers and other information] . ... HISI PTT data: size 4194304 bytes . 00000000: 00 00 00 00 Prefix . 00000004: 01 00 00 60 Header DW0 . 00000008: 0f 1e 00 01 Header DW1 . 0000000c: 04 00 00 00 Header DW2 . 00000010: 40 00 81 02 Header DW3 . 00000014: 33 c0 04 00 Time . 00000020: 00 00 00 00 Prefix . 00000024: 01 00 00 60 Header DW0 . 00000028: 0f 1e 00 01 Header DW1 . 0000002c: 04 00 00 00 Header DW2 . 00000030: 40 00 81 02 Header DW3 . 00000034: 02 00 00 00 Time . 00000040: 00 00 00 00 Prefix . 00000044: 01 00 00 60 Header DW0 . 00000048: 0f 1e 00 01 Header DW1 . 0000004c: 04 00 00 00 Header DW2 . 00000050: 40 00 81 02 Header DW3 [...]