[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 04:09:10 CET 2015

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.
Is this okay for your case?


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