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

[Shuai Xue]

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@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxx>
>>>>>>> Reported-by: kernel test robot <lkp@xxxxxxxxx>
>>>>>>> Link: https://lore.kernel.org/oe-kbuild-all/202305170639.XU3djFZX-lkp@xxxxxxxxx/
>>>>>>> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>>>>>
>>>>> 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