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

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Message-ID: <20221107152809.GE21002@willie-the-truck>
Date:   Mon, 7 Nov 2022 15:28:10 +0000
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 Fri, Sep 23, 2022 at 09:51:40PM +0800, Shuai Xue wrote:
> 
> 
> 在 2022/9/22 PM9:25, Will Deacon 写道:
> > 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.
> 
> Thank you for your valuable comments.
> 
> It's a good idea to encode bdf in bitmap and exposing a `bdf=' selector to userspace.
> The problem of bdf selector is that the user need to compute bdf from lanes, do you
> think it is user friendly? I'm worried about increasing the burden of users.

I don't see this as being an issue, particularly if you document how to do
it.

Will