Re: [PATCH v12 3/3] Documentation: tracing: Add documentation about PCI tracepoints

Ilpo Järvinen
2025-10-14T14:41:07Z

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On Tue, 14 Oct 2025, Shuai Xue wrote:

> The PCI tracing system provides tracepoints to monitor critical hardware
> events that can impact system performance and reliability. Add
> documentation about it.
>
> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
> ---
> Documentation/trace/events-pci.rst | 74 ++++++++++++++++++++++++++++++
> 1 file changed, 74 insertions(+)
> create mode 100644 Documentation/trace/events-pci.rst
>
> diff --git a/Documentation/trace/events-pci.rst b/Documentation/trace/events-pci.rst
> new file mode 100644
> index 000000000000..500b27713224
> --- /dev/null
> +++ b/Documentation/trace/events-pci.rst
> @@ -0,0 +1,74 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===========================
> +Subsystem Trace Points: PCI
> +===========================
> +
> +Overview
> +========
> +The PCI tracing system provides tracepoints to monitor critical hardware events
> +that can impact system performance and reliability. These events normally show
> +up here:
> +
> + /sys/kernel/tracing/events/pci
> +
> +Cf. include/trace/events/pci.h for the events definitions.
> +
> +Available Tracepoints
> +=====================
> +
> +pci_hp_event
> +------------
> +
> +Monitors PCI hotplug events including card insertion/removal and link
> +state changes.
> +::
> +
> + pci_hp_event "%s slot:%s, event:%s\n"
> +
> +**Event Types**:
> +
> +* ``LINK_UP`` - PCIe link established
> +* ``LINK_DOWN`` - PCIe link lost
> +* ``CARD_PRESENT`` - Card detected in slot
> +* ``CARD_NOT_PRESENT`` - Card removed from slot
> +
> +**Example Usage**:
> +
> + # Enable the tracepoint
> + echo 1> /sys/kernel/debug/tracing/events/pci/pci_hp_event/enable
> +
> + # Monitor events (the following output is generated when a device is hotplugged)
> + cat /sys/kernel/debug/tracing/trace_pipe
> + irq/51-pciehp-88 [001] ..... 1311.177459: pci_hp_event: 0000:00:02.0 slot:10, event:CARD_PRESENT
> +
> + irq/51-pciehp-88 [001] ..... 1311.177566: pci_hp_event: 0000:00:02.0 slot:10, event:LINK_UP
> +
> +pcie_link_event
> +---------------
> +
> +Monitors PCIe link speed changes and provides detailed link status information.
> +::
> +
> + pcie_link_event "%s type:%d, reason:%d, cur_bus_speed:%s, max_bus_speed:%s, width:%u, flit_mode:%u, status:%s\n"
> +
> +**Parameters**:
> +
> +* ``type`` - PCIe device type (4=Root Port, etc.)
> +* ``reason`` - Reason for link change:
> +
> + - ``0`` - Link retrain
> + - ``1`` - Bus enumeration
> + - ``2`` - Bandwidth controller enable
> + - ``3`` - Bandwidth controller IRQ

Maybe these two should be called "Bandwidth notification" as that's the
name of the underlying mechanism.

For the entire series,

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

> + - ``4`` - Hotplug event
> +
> +
> +**Example Usage**:
> +
> + # Enable the tracepoint
> + echo1 > /sys/kernel/debug/tracing/events/pci/pcie_link_event/enable
> +
> + # Monitor events (the following output is generated when a device is hotplugged)
> + cat /sys/kernel/debug/tracing/trace_pipe
> + irq/51-pciehp-88 [001] ..... 381.545386: pcie_link_event: 0000:00:02.0 type:4, reason:4, cur_bus_speed:2.5 GT/s PCIe, max_bus_speed:16.0 GT/s PCIe, width:1, flit_mode:0, status:DLLLA
>

--
i.