Re: [PATCH v9 7/8] docs: trace: Add HiSilicon PTT device driver documentation

From: Mathieu Poirier
Date: Wed Jul 06 2022 - 13:58:12 EST

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Hi,

I have started looking at this set.

On Mon, Jun 06, 2022 at 07:55:54PM +0800, Yicong Yang wrote:
> Document the introduction and usage of HiSilicon PTT device driver.
>
> Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> ---
> Documentation/trace/hisi-ptt.rst | 307 +++++++++++++++++++++++++++++++
> Documentation/trace/index.rst | 1 +

The "get_maintainer" script clearly indicates that Jonathan Corbet maintains the
Documentation directory and yet he is not CC'ed on this patch, nor is the
linux-doc mainling list. As such, it would not be possible to merge this
patchset.

> 2 files changed, 308 insertions(+)
> create mode 100644 Documentation/trace/hisi-ptt.rst
>
> diff --git a/Documentation/trace/hisi-ptt.rst b/Documentation/trace/hisi-ptt.rst
> new file mode 100644
> index 000000000000..0a3112244d40
> --- /dev/null
> +++ b/Documentation/trace/hisi-ptt.rst
> @@ -0,0 +1,307 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +======================================
> +HiSilicon PCIe Tune and Trace device
> +======================================
> +
> +Introduction
> +============
> +
> +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.
> +::
> +
> + /sys/devices/hisi_ptt<sicl_id>_<core_id>

All entries added to sysfs should have corresponding documentation. See [1] and
[2] for details and [3] for an example.

[1]. https://elixir.bootlin.com/linux/latest/source/Documentation/ABI/README
[2]. https://elixir.bootlin.com/linux/latest/source/Documentation/ABI/testing
[3]. https://elixir.bootlin.com/linux/latest/source/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x

> +
> +Tune
> +====
> +
> +PTT tune is designed for monitoring and adjusting PCIe link parameters (events).
> +Currently we support events in 4 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

These look overly long... How about watermark_rx and watermark_tx?

> + $ 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.
> +
> +- tx_path_rx_req_alloc_buf_level: watermark of Rx requested
> +- tx_path_tx_req_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.

This is useful documentation but it also should be found in the ABI
documentation referred to above.

> +
> +Trace
> +=====
> +
> +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.
> +
> +1. filter
> +---------
> +
> +The TLP headers to trace can be filtered by the Root Ports or the requester
> +ID of the endpoints, 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. The supported filters and
> +related values are outputted through `available_root_port_filters` and
> +`available_requester_filters` sysfs attributes for Root Ports and Requesters
> +respectively.
> +::
> +
> + $ cat available_root_port_filters
> + 0000:00:10.0 0x80001
> + 0000:00:11.0 0x80004
> + $ cat available_requester_filters
> + 0000:01:00.0 0x00100
> + 0000:01:00.1 0x00101

If I remember correctly, one of the rule for sysfs is one line per entry.

> +
> +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.
> +
> +If no filter is available, reading the related filter sysfs attribute
> +will get an empty string.
> +::
> +
> + $ cat available_root_port_filters
> +
> + $ cat available_requester_filters

Those too look overly long, and where to find them is not documented. As such
users have to guest that it must be somewhere under
/sys/devices/hisi_ptt<sicl_id>_<core_id>/.

More comments tomorrow.

Thanks,
Mathieu

> +
> +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 available filters.
> +
> +2. type
> +-------
> +
> +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.
> +
> +3. direction
> +------------
> +
> +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'b0000: reserved
> +- 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
> +
> +4. format
> +--------------
> +
> +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 ][24][23][22][21][ 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.
> +
> +6. decoding
> +-----------
> +
> +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
> + [...]
> diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
> index f9b7bcb5a630..dd423113b7b1 100644
> --- a/Documentation/trace/index.rst
> +++ b/Documentation/trace/index.rst
> @@ -32,3 +32,4 @@ Linux Tracing Technologies
> sys-t
> coresight/index
> user_events
> + hisi-ptt
> --
> 2.24.0
>

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