Re: [dpdk-dev] [RFC V1] examples/l3fwd-power: fix memory leak for rte_pci_device

[Huisong Li <lihuisong@huawei.com>]

在 2021/9/16 18:36, Thomas Monjalon 写道:
> 16/09/2021 10:01, Huisong Li:
>> 在 2021/9/8 15:20, Thomas Monjalon 写道:
>>> 08/09/2021 04:01, Huisong Li:
>>>> 在 2021/9/7 16:53, Thomas Monjalon 写道:
>>>>> 07/09/2021 05:41, Huisong Li:
>>>>>> Calling rte_eth_dev_close() will release resources of eth device and close
>>>>>> it. But rte_pci_device struct isn't released when app exit, which will lead
>>>>>> to memory leak.
>>>>> That's a PMD issue.
>>>>> When the last port of a PCI device is closed, the device should be freed.
>>>> Why is this a PMD problem? I don't understand.
>>> In the PMD close function, freeing of PCI device must be managed,
>>> so the app doesn't have to bother.
>> I know what you mean. Currently, there are two ways to close PMD device
>> (rte_eth_dev_close() and rte_dev_remove()).
>>
>> For rte_dev_remove(), eth device can be closed and rte_pci_device also
>> can be freed, so it can make app not care about that.
>>
>> But dev_close() is only used to close eth device, and nothing about
>> rte_pci_device is involved in the framework layer
>>
>> call stack of dev_close(). The rte_pci_device is allocated and
>> initialized when the rte_pci_bus scans "/sys/bus/pci/devices" directory.
>>
>> Generally, the PMD of eth devices operates on the basis of eth devices,
>> and rarely on rte_pci_device.
> No. The PMD is doing the relation between the PCI device and the ethdev port.

It seems that the ethdev layer can create eth devices based on 
rte_pci_device, but does not release rte_pci_device.

>
>> And the rte_pci_device corresponding to the eth devices managed and
>> processed by rte_pci_bus.
>>
>> So, PMD is closed only based on the port ID of the eth device, whilch
>> only shuts down eth devices, not frees rte_pci_device
>> and remove it from rte_pci_bus.
> Not really.
I do not see any PMD driver releasing rte_pci_device in dev_close().
> If there is no port using the PCI device, it should be released.
Yes.
>
>>>> As far as I know, most apps or examples in the DPDK project have only
>>>> one port for a pci device.
>>> The number of ports per PCI device is driver-specific.
>>>
>>>> When the port is closed, the rte_pci_device should be freed. But none of
>>>> the apps seem to do this.
>>> That's because from the app point of view, only ports should be managed.
>>> The hardware device is managed by the PMD.
>>> Only drivers (PMDs) have to do the relation between class ports
>>> and hardware devices.
>> Yes. But the current app only closes the port to disable the PMD, and
>> the rte_pci_device cannot be freed.
> Why not?
Because most apps in DPDK call dev_close() to close the eth device 
corresponding to a port.
>
>> Because rte_pci_device cannot be released in dev_close() of PMD, and is
>> managed by framework layer.
> No
>
>> Btw. Excluding rte_dev_probe() and rte_dev_remove(),  it seems that the
>> DPDK framework only automatically
>> scans PCI devices, but does not automatically release PCI devices when
>> the process exits.
> Indeed, because such freeing is the responsibility of the PMD.

Do you mean to free rte_pci_device in the dev_close() API?

How should PMD free it? What should we do? Any good suggestions?

Would it be more appropriate to do this in rte_eal_cleanup() if it 
cann't be done in the API above?
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