Re: [dpdk-dev] [PATCH] net/vdev_netvsc: handle removal of associated pci device

[Long Li <longli@microsoft.com>]

>Subject: Re: [dpdk-dev] [PATCH] net/vdev_netvsc: handle removal of
>associated pci device
>
>Hi Stephen
>
>From: Stephen Hemminger:
>> On Sun, 6 Sep 2020 12:38:18 +0000
>> Matan Azrad <matan@nvidia.com> wrote:
>>
>> > Hi Stephen
>> >
>> > From: Stephen Hemminger:
>> > > The vdev_netvsc was not detecting when the associated PCI device
>> > > (SRIOV) was removed. Because of that it would keep feeding the
>> > > same
>> > > (removed) device to failsafe PMD which would then unsuccessfully
>> > > try and probe for it.
>> > >
>> > > Change to use a mark/sweep method to detect that PCI device was
>> > > removed, and also only tell failsafe about new PCI devices.
>> > > Vdev_netvsc does not have to keep stuffing the pipe with the same
>> > > already existing PCI device.
>> >
>> > As I know, the vdev_netvsc driver doesn't call to failsafe if the
>> > PCI device is
>> not detected by the readlink command(considered as removed)...
>> > Am I missing something?
>>
>> The original code is broken because ctx_yield is not cleared, it keeps
>> sending the same value.
>
>Looking on the code again, It looks like ctx->yield has no effect on the next
>pipe write, It is just used for log.
>
>After the PCI interface matching to the netvsc interface, the pipe write is
>triggered only if the readlink commands success to see the plugged-in PCI
>device:
>readlink /sys/class/net/[iface]/device/subsystem shows "pci"
>readlink /sys/class/net/[iface]/device shows the pci device ID.
>
>So, the assumption is when the above readlink failed on the interface the
>device is removed(plugged-out) and the fd write will not happen.
>
>The code will continue to retry probe again and again until success only for
>plugged-in pci device matched the netvsc device.

Hi Matan,

The original code keeps writing to pipe even it's the same PCI device. The new code writes to pipe for a new device, only once. See the following code:

+	/* Skip if this is same device already sent to failsafe */
+	if (strcmp(addr, ctx->yield) == 0)
+		return 0;

This patch also saves lots of CPU since it no longer writes to pipe all the time. You are correct about the code will continue to probe on a new PCI device. But someone has to do it to handle hot-add.

Thanks,
Long


>
>> It looks like device removal and add was never tested.
>
>This is basic test we have to test plug-in plug-out and it passed every day in
>the last years.
>
>Maybe something new and special in your setup?
>
>> If you test removal you will see that vdev_netvsc:
>>  1. Sends same PCI device repeatedly to failsafe (every alarm call)
>>     This is harmless, but useless.
>>  2. When device is removed, keeps doing #1