Re: [PATCH] vhost: Fix retrieval of numa information in PMD

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Wed, Apr 06, 2016 at 03:49:25PM +0900, Tetsuya Mukawa wrote:
> On 2016/04/06 1:09, Ciara Loftus wrote:
> > After some testing, it was found that retrieving numa information
> > about a vhost device via a call to get_mempolicy is more
> > accurate when performed during the new_device callback versus
> > the vring_state_changed callback, in particular upon initial boot
> > of the VM.  Performing this check during new_device is also
> > potentially more efficient as this callback is only triggered once
> > during device initialisation, compared with vring_state_changed
> > which may be called multiple times depending on the number of
> > queues assigned to the device.
> >
> > Reorganise the code to perform this check and assign the correct
> > socket_id to the device during the new_device callback.
> >
> > Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
> > ---
> >  drivers/net/vhost/rte_eth_vhost.c | 28 ++++++++++++++--------------
> >  1 file changed, 14 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/net/vhost/rte_eth_vhost.c b/drivers/net/vhost/rte_eth_vhost.c
> > index 4cc6bec..b1eb082 100644
> > --- a/drivers/net/vhost/rte_eth_vhost.c
> > +++ b/drivers/net/vhost/rte_eth_vhost.c
> >
> 
> Hi,
> 
> I appreciate fixing it.
> Just one worry is that state changed event may be occurred before new
> device event.
> The users should not call rte_eth_dev_socket_id() until new device event
> comes, even if they catch queue state events.
> Otherwise, they will get wrong socket id to call
> rte_eth_rx/tx_queue_setup().

There is no way to guarantee that the socket id stuff would work
perfectly in vhost, right? I mean, it's likely that virtio device
would allocate memory from 2 or more sockets.

So, it doesn't matter too much whether it's set perfectly right
or not. Instead, we should assign it with a saner value instead
of a obvious wrong one when new_device() is not invoked yet. So,
I'd suggest to make an assignment first based on vhost_dev (or
whatever) struct, and then make it "right" at new_device()
callback?

> So how about commenting it in 'rte_eth_vhost.h'?

It asks a different usage than other PMDs, which I don't think
it's a good idea.

	--yliu