Re: [PATCH v8] PCI: hotplug: Add a generic RAS tracepoint for hotplug event

[Shuai Xue <xueshuai@linux.alibaba.com>]

Hi, Ilpo,

在 2025/5/20 01:10, Ilpo Järvinen 写道:
> On Mon, 12 May 2025, Shuai Xue wrote:
> 
>> Hotplug events are critical indicators for analyzing hardware health,
>> particularly in AI supercomputers where surprise link downs can
>> significantly impact system performance and reliability.
>>
>> To this end, define a new TRACING_SYSTEM named pci, add a generic RAS
>> tracepoint for hotplug event to help healthy check, and generate
>> tracepoints for pcie hotplug event. Add enum pci_hotplug_event in
>> include/uapi/linux/pci.h so applications like rasdaemon can register
>> tracepoint event handlers for it.
>>
>> The output like below:
>>
>> $ echo 1 > /sys/kernel/debug/tracing/events/pci/pci_hp_event/enable
>> $ cat /sys/kernel/debug/tracing/trace_pipe
>>      <...>-206     [001] .....    40.373870: pci_hp_event: 0000:00:02.0 slot:10, event:Link Down
>>
>>      <...>-206     [001] .....    40.374871: pci_hp_event: 0000:00:02.0 slot:10, event:Card not present
>>
>> Suggested-by: Lukas Wunner <lukas@wunner.de>
>> Suggested-by: Steven Rostedt <rostedt@goodmis.org>
>> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
>> Reviewed-by: Lukas Wunner <lukas@wunner.de>
>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>> ---
>> changes since v7:
>> - replace the TRACE_INCLUDE_PATH to avoid macro conflict per Steven
>> - pick up Reviewed-by from Lukas Wunner
>> ---
>>   drivers/pci/hotplug/Makefile      |  3 ++
>>   drivers/pci/hotplug/pciehp_ctrl.c | 33 ++++++++++++---
>>   drivers/pci/hotplug/trace.h       | 68 +++++++++++++++++++++++++++++++
>>   include/uapi/linux/pci.h          |  7 ++++
>>   4 files changed, 105 insertions(+), 6 deletions(-)
>>   create mode 100644 drivers/pci/hotplug/trace.h
>>
>> diff --git a/drivers/pci/hotplug/Makefile b/drivers/pci/hotplug/Makefile
>> index 40aaf31fe338..a1a9d1e98962 100644
>> --- a/drivers/pci/hotplug/Makefile
>> +++ b/drivers/pci/hotplug/Makefile
>> @@ -3,6 +3,9 @@
>>   # Makefile for the Linux kernel pci hotplug controller drivers.
>>   #
>>   
>> +# define_trace.h needs to know how to find our header
>> +CFLAGS_pciehp_ctrl.o				:= -I$(src)
>> +
>>   obj-$(CONFIG_HOTPLUG_PCI)		+= pci_hotplug.o
>>   obj-$(CONFIG_HOTPLUG_PCI_COMPAQ)	+= cpqphp.o
>>   obj-$(CONFIG_HOTPLUG_PCI_IBM)		+= ibmphp.o
>> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
>> index d603a7aa7483..f9beb4d3a9b8 100644
>> --- a/drivers/pci/hotplug/pciehp_ctrl.c
>> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
>> @@ -23,6 +23,9 @@
>>   #include "../pci.h"
>>   #include "pciehp.h"
>>   
>> +#define CREATE_TRACE_POINTS
>> +#include "trace.h"
>> +
>>   /* The following routines constitute the bulk of the
>>      hotplug controller logic
>>    */
>> @@ -244,12 +247,20 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
>>   	case ON_STATE:
>>   		ctrl->state = POWEROFF_STATE;
>>   		mutex_unlock(&ctrl->state_lock);
>> -		if (events & PCI_EXP_SLTSTA_DLLSC)
>> +		if (events & PCI_EXP_SLTSTA_DLLSC) {
>>   			ctrl_info(ctrl, "Slot(%s): Link Down\n",
>>   				  slot_name(ctrl));
>> -		if (events & PCI_EXP_SLTSTA_PDC)
>> +			trace_pci_hp_event(pci_name(ctrl->pcie->port),
>> +					   slot_name(ctrl),
>> +					   PCI_HOTPLUG_LINK_DOWN);
>> +		}
>> +		if (events & PCI_EXP_SLTSTA_PDC) {
>>   			ctrl_info(ctrl, "Slot(%s): Card not present\n",
>>   				  slot_name(ctrl));
>> +			trace_pci_hp_event(pci_name(ctrl->pcie->port),
>> +					   slot_name(ctrl),
>> +					   PCI_HOTPLUG_CARD_NOT_PRESENT);
>> +		}
>>   		pciehp_disable_slot(ctrl, SURPRISE_REMOVAL);
>>   		break;
>>   	default:
>> @@ -269,6 +280,9 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
>>   					      INDICATOR_NOOP);
>>   			ctrl_info(ctrl, "Slot(%s): Card not present\n",
>>   				  slot_name(ctrl));
>> +			trace_pci_hp_event(pci_name(ctrl->pcie->port),
>> +					   slot_name(ctrl),
>> +					   PCI_HOTPLUG_CARD_NOT_PRESENT);
>>   		}
>>   		mutex_unlock(&ctrl->state_lock);
>>   		return;
>> @@ -281,12 +295,19 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
>>   	case OFF_STATE:
>>   		ctrl->state = POWERON_STATE;
>>   		mutex_unlock(&ctrl->state_lock);
>> -		if (present)
>> +		if (present) {
>>   			ctrl_info(ctrl, "Slot(%s): Card present\n",
>>   				  slot_name(ctrl));
>> -		if (link_active)
>> -			ctrl_info(ctrl, "Slot(%s): Link Up\n",
>> -				  slot_name(ctrl));
>> +			trace_pci_hp_event(pci_name(ctrl->pcie->port),
>> +					   slot_name(ctrl),
>> +					   PCI_HOTPLUG_CARD_PRESENT);
>> +		}
>> +		if (link_active) {
>> +			ctrl_info(ctrl, "Slot(%s): Link Up\n", slot_name(ctrl));
>> +			trace_pci_hp_event(pci_name(ctrl->pcie->port),
>> +					   slot_name(ctrl),
>> +					   PCI_HOTPLUG_LINK_UP);
>> +		}
>>   		ctrl->request_result = pciehp_enable_slot(ctrl);
>>   		break;
>>   	default:
>> diff --git a/drivers/pci/hotplug/trace.h b/drivers/pci/hotplug/trace.h
>> new file mode 100644
>> index 000000000000..21329c198019
>> --- /dev/null
>> +++ b/drivers/pci/hotplug/trace.h
>> @@ -0,0 +1,68 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#if !defined(_TRACE_HW_EVENT_PCI_HP_H) || defined(TRACE_HEADER_MULTI_READ)
>> +#define _TRACE_HW_EVENT_PCI_HP_H
>> +
>> +#include <linux/tracepoint.h>
>> +
>> +#undef TRACE_SYSTEM
>> +#define TRACE_SYSTEM pci
>> +
>> +#define PCI_HOTPLUG_EVENT					\
>> +	EM(PCI_HOTPLUG_LINK_UP,			"Link Up")	\
>> +	EM(PCI_HOTPLUG_LINK_DOWN,		"Link Down")	\
>> +	EM(PCI_HOTPLUG_CARD_PRESENT,		"Card present")	\
>> +	EMe(PCI_HOTPLUG_CARD_NOT_PRESENT,	"Card not present")
> 
> Hi,
> 
> While I was thinking of adding tracing into PCIe BW controller (bwctrl),
> I ended up thinking that perhaps it would make more sense to have PCIe
> Link related tracepoints which would cover both hotplug and bwctrl so that
> also Link Speed changes would be reported through the same trace event.
> 
> Downgraded speed may indicate there's something wrong with the card and
> the Link Speed does have performance impact too for those who are pushing
> BW boundaries such as AI systems.

Agreed!

> 
> So my suggestion is:
> 
> - Add "Link Speed changed" to the event types.
> - Add Link Speed and Width into the event format (and probably also Flit
>    mode as PCIe gen6 is coming).


How about bellow event format:

+	TP_STRUCT__entry(
+		__string(	port_name,	port_name	)
+		__field(	unsigned char,	cur_bus_speed	)
+		__field(	unsigned char,	max_bus_speed	)
+		__field(	unsigned char,	flit_mode	)
+	),

And add the event to pcie_update_link_speed():

@@ -796,6 +799,10 @@ void pcie_update_link_speed(struct pci_bus *bus)
         pcie_capability_read_word(bridge, PCI_EXP_LNKSTA, &linksta);
         pcie_capability_read_word(bridge, PCI_EXP_LNKSTA2, &linksta2);
         __pcie_update_link_speed(bus, linksta, linksta2);
+
+       trace_pci_link_event(pci_name(bridge), bus->cur_bus_speed,
+                                          bus->max_bus_speed,
+                                          PCI_HOTPLUG_LINK_SPEED_CHANGED);

But I don't find link speed changed in hotplug driver, and the
format of "Link Speed changed" is a bit different from "pci_hp_event".

Do we really need a PCI_HOTPLUG_EVENT? May PCI_LINK_EVENT is more
appropriate?

Thanks.
Best Regards.
Shuai