[dpdk-dev] [PATCH v5 1/3] vhost: Add callback and private data for vhost PMD

Tetsuya Mukawa mukawa at igel.co.jp
Thu Dec 24 04:54:08 CET 2015

On 2015/12/24 12:09, Tetsuya Mukawa wrote:
> On 2015/12/22 13:47, Rich Lane wrote:
>> On Mon, Dec 21, 2015 at 7:41 PM, Yuanhan Liu <yuanhan.liu at linux.intel.com>
>> wrote:
>>> On Fri, Dec 18, 2015 at 10:01:25AM -0800, Rich Lane wrote:
>>>> I'm using the vhost callbacks and struct virtio_net with the vhost PMD
>>> in a few
>>>> ways:
>>> Rich, thanks for the info!
>>>> 1. new_device/destroy_device: Link state change (will be covered by the
>>> link
>>>> status interrupt).
>>>> 2. new_device: Add first queue to datapath.
>>> I'm wondering why vring_state_changed() is not used, as it will also be
>>> triggered at the beginning, when the default queue (the first queue) is
>>> enabled.
>> Turns out I'd misread the code and it's already using the
>> vring_state_changed callback for the
>> first queue. Not sure if this is intentional but vring_state_changed is
>> called for the first queue
>> before new_device.
>>>> 3. vring_state_changed: Add/remove queue to datapath.
>>>> 4. destroy_device: Remove all queues (vring_state_changed is not called
>>> when
>>>> qemu is killed).
>>> I had a plan to invoke vring_state_changed() to disable all vrings
>>> when destroy_device() is called.
>> That would be good.
>>>> 5. new_device and struct virtio_net: Determine NUMA node of the VM.
>>> You can get the 'struct virtio_net' dev from all above callbacks.
>>> 1. Link status interrupt.
>>> To vhost pmd, new_device()/destroy_device() equals to the link status
>>> interrupt, where new_device() is a link up, and destroy_device() is link
>>> down().
>>>> 2. New queue_state_changed callback. Unlike vring_state_changed this
>>> should
>>>> cover the first queue at new_device and removal of all queues at
>>>> destroy_device.
>>> As stated above, vring_state_changed() should be able to do that, except
>>> the one on destroy_device(), which is not done yet.
>>>> 3. Per-queue or per-device NUMA node info.
>>> You can query the NUMA node info implicitly by get_mempolicy(); check
>>> numa_realloc() at lib/librte_vhost/virtio-net.c for reference.
>> Your suggestions are exactly how my application is already working. I was
>> commenting on the
>> proposed changes to the vhost PMD API. I would prefer to
>> and rte_eth_dev_socket_id for consistency with other NIC drivers, instead
>> of these vhost-specific
>> hacks. The queue state change callback is the one new API that needs to be
>> added because
>> normal NICs don't have this behavior.
>> You could add another rte_eth_event_type for the queue state change
>> callback, and pass the
>> queue ID, RX/TX direction, and enable bit through cb_arg. 
> Hi Rich,
> So far, EAL provides rte_eth_dev_callback_register() for event handling.
> DPDK app can register callback handler and "callback argument".
> And EAL will call callback handler with the argument.
> Anyway, vhost library and PMD cannot change the argument.
> I guess the callback handler will need to call ethdev APIs to know what
> causes the interrupt.
> Probably rte_eth_dev_socket_id() is to know numa_node, and
> rte_eth_dev_info_get() is to know the number of queues.

It seems rte_eth_dev_info_get() is not enough, because DPDK application
needs not only the number of queues, but also which queues are enabled
or disabled at least.
I guess current interrupt mechanism and ethdev APIs cannot provides such
information, because it's something special for vhost case.


> Is this okay for your case?
> Thanks,
> Tetsuya

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