linux-kernel - Re: [PATCH v3 1/3] docs: perf: Add description for Synopsys DesignWare PCIe PMU driver

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Message-ID: <20230516153233.000032f3@Huawei.com>
Date:   Tue, 16 May 2023 15:32:33 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Shuai Xue <xueshuai@...ux.alibaba.com>
CC:     <helgaas@...nel.org>, <yangyicong@...wei.com>, <will@...nel.org>,
        <baolin.wang@...ux.alibaba.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <rdunlap@...radead.org>, <robin.murphy@....com>,
        <mark.rutland@....com>, <zhuo.song@...ux.alibaba.com>
Subject: Re: [PATCH v3 1/3] docs: perf: Add description for Synopsys
 DesignWare PCIe PMU driver

On Mon, 17 Apr 2023 14:17:27 +0800
Shuai Xue <xueshuai@...ux.alibaba.com> wrote:

> Alibaba's T-Head Yitan 710 SoC is built on Synopsys' widely deployed and
> silicon-proven DesignWare Core PCIe controller which implements PMU for

Keep to most relevant facts in description only.  Something like:

Alibaba's T-Head Yitan 710 SoC includes Synopsys' DesignWare Core PCIe controller
which implements ...

Or ask for advertising fees from Synopsys :)


> performance and functional debugging to facilitate system maintenance.
> Document it to provide guidance on how to use it.
> 
> Signed-off-by: Shuai Xue <xueshuai@...ux.alibaba.com>
> ---
>  .../admin-guide/perf/dwc_pcie_pmu.rst         | 61 +++++++++++++++++++
>  Documentation/admin-guide/perf/index.rst      |  1 +
>  2 files changed, 62 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..0672e959ebe4
> --- /dev/null
> +++ b/Documentation/admin-guide/perf/dwc_pcie_pmu.rst
> @@ -0,0 +1,61 @@
> +======================================================================
> +Synopsys DesignWare Cores (DWC) PCIe Performance Monitoring Unit (PMU)
> +======================================================================
> +
> +DesignWare Cores (DWC) PCIe PMU
> +===============================
> +
> +To facilitate collection of statistics, Synopsys DesignWare Cores PCIe
> +controller provides the following two features:
> +
> +- Time Based Analysis (RX/TX data throughput and time spent in each
> +  low-power LTSSM state)
> +- Lane Event counters (Error and Non-Error for lanes)
> +
> +The PMU is not a PCIe Root Complex integrated End Point (RCiEP) device but
> +only register counters provided by each PCIe Root Port.
> +
> +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 counters are 64-bit width and measure data in two categories,
> +
> +- percentage of time does the controller stay in LTSSM state in a
> +  configurable duration. The measurement range of each Event in Group#0.
> +- amount of data processed (Units of 16 bytes). The measurement range of
> +  each Event in Group#1.
> +
> +Lane Event counters
> +-------------------
> +
> +Using this feature you can obtain Error and Non-Error information in
> +specific lane by the controller.
> +
> +The counters are 32-bit width and the measured event is select by:
> +
> +- Group i
> +- Event j within the Group i
> +- and Lane k
> +
> +Some of the event counters only exist for specific configurations.
> +
> +DesignWare Cores (DWC) PCIe PMU Driver
> +=======================================
> +
> +This driver add PMU devices for each PCIe Root Port. And the PMU device is
> +named based the BDF of 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.
I'd suggest renaming to a scheme lie
dwc_rootport_30:03.0 
to save people remembering how to break up the BDF parts.
 
> +
> +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/
> +
> +average RX bandwidth can be calculated like this:
> +
> +    PCIe TX Bandwidth = PCIE_TX_DATA * 16B / Measure_Time_Window

Could consider an example of the other type of event, the error counters
you mention.

Otherwise, looks good to me.

Jonathan

> diff --git a/Documentation/admin-guide/perf/index.rst b/Documentation/admin-guide/perf/index.rst
> index 9de64a40adab..11a80cd28a2e 100644
> --- a/Documentation/admin-guide/perf/index.rst
> +++ b/Documentation/admin-guide/perf/index.rst
> @@ -19,5 +19,6 @@ Performance monitor support
>     arm_dsu_pmu
>     thunderx2-pmu
>     alibaba_pmu
> +   dwc_pcie_pmu
>     nvidia-pmu
>     meson-ddr-pmu