linux-kernel - Re: [PATCH v1 1/3] docs: perf: Add description for Synopsys DesignWare PCIe PMU driver

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Message-ID: <20220922132543.GA12095@willie-the-truck>
Date:   Thu, 22 Sep 2022 14:25:44 +0100
From:   Will Deacon <will@...nel.org>
To:     Shuai Xue <xueshuai@...ux.alibaba.com>
Cc:     Jonathan.Cameron@...wei.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, rdunlap@...radead.org,
        robin.murphy@....com, mark.rutland@....com,
        baolin.wang@...ux.alibaba.com, zhuo.song@...ux.alibaba.com
Subject: Re: [PATCH v1 1/3] docs: perf: Add description for Synopsys
 DesignWare PCIe PMU driver

On Sat, Sep 17, 2022 at 08:10:34PM +0800, Shuai Xue 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
> 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..fbcbf10b23b7
> --- /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 Lank 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,
> +
> +    10:00.0 PCI bridge: Device 1ded:8000 (rev 01)
> +
> +the PMU device name for this Root Port is pcie_bdf_100000.
> +
> +Example usage of counting PCIe RX TLP data payload (Units of 16 bytes)::
> +
> +    $# perf stat -a -e pcie_bdf_200/Rx_PCIe_TLP_Data_Payload/

Do you really need to expose a separate PMU instance to userspace for each
BDF? I think it would be much cleaner if you could follow the approach used
by hisilicon/hisi_pcie_pmu.c and hide these details in the driver, exposing
a `bdf=' selector to userspace instead.

Will