Re: [PATCH v8 1/4] docs: perf: Add description for Synopsys DesignWare PCIe PMU driver

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Tue, 17 Oct 2023 09:32:32 +0800
Shuai Xue <xueshuai@linux.alibaba.com> wrote:

> Alibaba's T-Head Yitan 710 SoC includes Synopsys' DesignWare Core PCIe
> controller which implements which implements PMU for performance and
> functional debugging to facilitate system maintenance.
> 
> Document it to provide guidance on how to use it.
> 
> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

A few minor things inline and one question that I'd like a comment on
for my understanding at least! (why not multiply the counter by 16 and
make the maths simpler?)

With those tidied up,
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Thanks,

Jonathan


> ---
>  .../admin-guide/perf/dwc_pcie_pmu.rst         | 94 +++++++++++++++++++
>  Documentation/admin-guide/perf/index.rst      |  1 +
>  2 files changed, 95 insertions(+)
>  create mode 100644 Documentation/admin-guide/perf/dwc_pcie_pmu.rst
> 
> diff --git a/Documentation/admin-guide/perf/dwc_pcie_pmu.rst b/Documentation/admin-guide/perf/dwc_pcie_pmu.rst
> new file mode 100644
> index 000000000000..eac1b6f36450
> --- /dev/null
> +++ b/Documentation/admin-guide/perf/dwc_pcie_pmu.rst
> @@ -0,0 +1,94 @@
> +======================================================================
> +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 select by:
> +
> +- Group i
> +- Event j within the Group i
> +- and Lane k
The and here is a little confusing. I'd rework as
The PMU event is selected by all of:
- Group i
- Event j within the Group i
- Lane k

> +
> +Some of the event only exist for specific configurations.

events

> +
> +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 16 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 = PCIE_RX_DATA * 16B / Measure_Time_Window
> +    PCIe TX Bandwidth = PCIE_TX_DATA * 16B / Measure_Time_Window

Silly question (sorry I didn't raise it earlier) but can we make the interface
more intuitive by just multiplying the counter value at point of read by 16?

> +
> +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.
> diff --git a/Documentation/admin-guide/perf/index.rst b/Documentation/admin-guide/perf/index.rst
> index f60be04e4e33..6bc7739fddb5 100644
> --- a/Documentation/admin-guide/perf/index.rst
> +++ b/Documentation/admin-guide/perf/index.rst
> @@ -19,6 +19,7 @@ Performance monitor support
>     arm_dsu_pmu
>     thunderx2-pmu
>     alibaba_pmu
> +   dwc_pcie_pmu
>     nvidia-pmu
>     meson-ddr-pmu
>     cxl


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