Linux Virtualization - Jan 2014 - [PATCH net-next v2 4/4] virtio-net: initial debugfs support, export mergeable rx buffer size

On Mon, 2014-01-13 at 11:40 +0200, Michael S. Tsirkin
wrote:
> On Sun, Jan 12, 2014 at 03:32:28PM -0800, Michael Dalton wrote:
[...]
> > The last issue is how the rx_queue_attribute 'show' function
> > implementation for mergeable_rx_buffer_size will access the
appropriate
> > per-receive queue EWMA data. The arguments to the show function will
be
> > the netdev_rx_queue and the attribute itself. We can get to the
> > struct net_device from the netdev_rx_queue.  If we extended
> > netdev_rx_queue to indicate the queue_index or to store a void
*priv_data
> > pointer, that would be sufficient to allow us to resolve this issue.
> 
> Hmm netdev_rx_queue is not defined unless CONFIG_RPS is set.
> Maybe we should use a different structure.
[...]

I don't think RPS should own this structure.  It's just that there are
currently no per-RX-queue attributes other than those defined by RPS.

By the way, CONFIG_RPS is equivalent to CONFIG_SMP so will likely be
enabled already in most places where virtio_net is used.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

On Mon, Jan 13, 2014 at 7:38 AM, Ben Hutchings <bhutchings at
solarflare.com>
wrote:
> I don't think RPS should own this structure.  It's just that there
are
> currently no per-RX-queue attributes other than those defined by RPS.
Agreed, there is useful attribute-independent functionality already
built around netdev_rx_queue - e.g., dynamically resizing the rx queue
kobjs as the number of RX queues enabled for the netdev is changed. While
the current attributes happen to be used only by RPS, AFAICT it seems
RPS should not own netdev_rx_queue but rather should own the RPS-specific
fields themselves within netdev_rx_queue.

If there are no objections, it seems like I could modify
netdev_rx_queue and related functionality so that their existence does
not depend on CONFIG_RPS, and instead just have CONFIG_RPS control
whether or not the RPS-specific attributes/fields are present.

Best,

Mike

Sorry I missed this important piece of information, it appears that
netdev_queue (the TX equivalent of netdev_rx_queue) already has
decoupled itself from CONFIG_XPS due to an attribute,
queue_trans_timeout, that does not depend on XPS functionality. So it
seems that something somewhat equivalent has already happened on the
TX side.

Best,

Mike