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

[Huisong Li <lihuisong@huawei.com>]

Hi, Thomas

The new comments are as follows, and look forward to your reply. Thanks!


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.

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.

>
>> 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.

Because rte_pci_device cannot be released in dev_close() of PMD, and is 
managed by framework layer.


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.

Above "automatic", I means that it doesn't involve apps or PMDs.

>
>>>> +		/* Retrieve device address in eth device before closing it. */
>>>> +		eth_dev = &rte_eth_devices[portid];
>>> You should not access this array, considered internal.
>> We have to save the address of rte_device to free rte_pci_device before
>> closing eth device.
>>
>> Because the the device address in rte_eth_dev struct will be set to a
>> NULL after closing eth device.
>>
>> It's also handled in OVS in this way.
> No you don't have to call rte_dev_remove at all from an app.
>
>>>> +		rte_dev = eth_dev->device;
>>>>    		rte_eth_dev_close(portid);
>>>> +		ret = rte_dev_remove(rte_dev);
>
>
> .