Re: [PATCH v6 3/4] drivers/perf: add DesignWare PCIe PMU driver

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

On 2023/8/4 11:09, Shuai Xue wrote:
> 
> 
> On 2023/8/4 10:28, Yicong Yang wrote:
>> On 2023/8/4 9:39, Shuai Xue wrote:
>>>
>>>
>>> On 2023/8/1 19:46, Yicong Yang wrote:
>>>> On 2023/7/28 20:41, Shuai Xue wrote:
>>>>>
>>>>>
>>>>> On 2023/7/27 17:39, Jonathan Cameron wrote:
>>>>>> On Tue, 6 Jun 2023 23:14:07 +0800
>>>>>> Yicong Yang <yangyicong@huawei.com> wrote:
>>>>>>
>>>>>>> On 2023/6/6 15:49, Shuai Xue wrote:
>>>>>>>> This commit adds the PCIe Performance Monitoring Unit (PMU) driver support
>>>>>>>> for T-Head Yitian SoC chip. Yitian is based on the Synopsys PCI Express
>>>>>>>> Core controller IP which provides statistics feature. The PMU is not a PCIe
>>>>>>>> Root Complex integrated End Point(RCiEP) device but only register counters
>>>>>>>> provided by each PCIe Root Port.
>>>>>>>>
>>>>>>>> To facilitate collection of statistics the controller provides the
>>>>>>>> following two features for each Root Port:
>>>>>>>>
>>>>>>>> - Time Based Analysis (RX/TX data throughput and time spent in each
>>>>>>>>   low-power LTSSM state)
>>>>>>>> - Event counters (Error and Non-Error for lanes)
>>>>>>>>
>>>>>>>> Note, only one counter for each type and does not overflow interrupt.
>>>>>>>>
>>>>>>>> This driver adds 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.
>>>>>>>>
>>>>>>>> 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
>>>>>>>>
>>>>>>>> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
>>>>>>>> Reported-by: kernel test robot <lkp@intel.com>
>>>>>>>> Link: https://lore.kernel.org/oe-kbuild-all/202305170639.XU3djFZX-lkp@intel.com/
>>>>>>>> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>>>>>>
>>>>>> I'll review on top to avoid any duplication with Yicong.
>>>>>
>>>>> Thank you! It also served as a reminder that I missed Yicong's email. It appears
>>>>> that Thunderbird mistakenly moved his email to the junk folder, resulting in me
>>>>> overlooking it.
>>>>>
>>>>>>
>>>>>> Note I've cropped the stuff neither of us commented on so it's
>>>>>> easier to spot the feedback.
>>>>>
>>>>> Thank you for noting that. My feedback is replied inline.
>>>>>
>>>>>>
>>>>>> Jonathan
>>>>>>
>>>>>>>> ---
>>>>>>>>  drivers/perf/Kconfig        |   7 +
>>>>>>>>  drivers/perf/Makefile       |   1 +
>>>>>>>>  drivers/perf/dwc_pcie_pmu.c | 706 ++++++++++++++++++++++++++++++++++++
>>>>>>>>  3 files changed, 714 insertions(+)
>>>>>>>>  create mode 100644 drivers/perf/dwc_pcie_pmu.c
>>>>>>>>
>>>>>>>> diff --git a/drivers/perf/Kconfig b/drivers/perf/Kconfig
>>>>>>>> index 711f82400086..6ff3921d7a62 100644
>>>>>>>> --- a/drivers/perf/Kconfig
>>>>>>>> +++ b/drivers/perf/Kconfig
>>>>>>>> @@ -209,6 +209,13 @@ config MARVELL_CN10K_DDR_PMU
>>>>>>>>  	  Enable perf support for Marvell DDR Performance monitoring
>>>>>>>>  	  event on CN10K platform.
>>>>>>>>  
>>>>>>>> +config DWC_PCIE_PMU
>>>>>>>> +	tristate "Enable Synopsys DesignWare PCIe PMU Support"
>>>>>>>> +	depends on (ARM64 && PCI)
>>>>>>>> +	help
>>>>>>>> +	  Enable perf support for Synopsys DesignWare PCIe PMU Performance
>>>>>>>> +	  monitoring event on Yitian 710 platform.
>>>>>>
>>>>>> The documentation kind of implies this isn't platform specific.
>>>>>> If some parts are (such as which events exist) then you may want to push
>>>>>> that to userspace / perftool with appropriate matching against specific SoC.
>>>>>>
>>>>>> If it is generic, then change this text to "event on platform including the Yitian 710."
>>>>>
>>>>> It is generic without any platform specific, so I will change it as you expected.
>>>>>
>>>>>>
>>>>>>>> +
>>>>>>>>  source "drivers/perf/arm_cspmu/Kconfig"
>>>>>>>>  
>>>>>>>>  source "drivers/perf/amlogic/Kconfig"
>>>>>>
>>>>>>>> new file mode 100644
>>>>>>>> index 000000000000..8bfcf6e0662d
>>>>>>>> --- /dev/null
>>>>>>>> +++ b/drivers/perf/dwc_pcie_pmu.c
>>>>>>>> @@ -0,0 +1,706 @@
>>>>>>
>>>>>> ...
>>>>>>
>>>>>>>> +
>>>>>>>> +struct dwc_pcie_pmu {
>>>>>>>> +	struct pci_dev		*pdev;		/* Root Port device */  
>>>>>>>
>>>>>>> If the root port removed after the probe of this PCIe PMU driver, we'll access the NULL
>>>>>>> pointer. I didn't see you hold the root port to avoid the removal.
>>>>>
>>>>> Do you mean that I should have a reference count of rootport by pci_dev_get() when allocating
>>>>> pcie_pmu?
>>>>>
>>>>>      pcie_pmu->pdev = pci_dev_get();
>>>>
>>>> It could be one option, but will block the removal of device from userspace. Another option
>>>> is to register a PCI bus notifier then on removal/added the driver can get notified and handle
>>>> it, for example, remove the related PMU on the removal of the root ports.
>>>
>>> I see, but can root port be removed from userspace? I check the hotplug slot interface, no root
>>> port is available to power off.
>>>
>>
>> For hotplug maybe not, but user can remove certian device through sysfs:
>>
>> echo 1 > /sys/bus/pci/devices/<root port>/remove
>>
> 
> Thank you, I will add a notifier for removal/added action.
> 
> Best Regards,
> Shuai

Hi, Yicong,

I am confused when adding a notifier by bus_register_notifier(). If I have added a action to
pdev->dev to unregister pmu:

		ret = perf_pmu_register(&pcie_pmu->pmu, name, -1);
		if (ret) {
			pci_err(pcie_pmu->pdev,
				"Error %d registering PMU @%x\n", ret, bdf);
			goto out;
		}
		ret = devm_add_action_or_reset(
			&pdev->dev, dwc_pcie_pmu_unregister_pmu, &pcie_pmu->pmu);

the pmu will be unregister when the port removes, so accessing the NULL pointer will never happen,
right? Do we still need the bus_register_notifier()?

Thank you.

Best Regards,
Shuai