Re: [PATCH net-next] virito-net: set queues after reset during xdp_set

[Jason Wang]

On 2017年02月19日 13:08, Michael S. Tsirkin wrote:

-       oxdp_qp = vi->xdp_queue_pairs;
-
        /* Changing the headroom in buffers is a disruptive operation because
         * existing buffers must be flushed and reallocated. This will happen
         * when a xdp program is initially added or xdp is disabled by removing
         * the xdp program resulting in number of XDP queues changing.
         */
        if (vi->xdp_queue_pairs != xdp_qp) {
-               vi->xdp_queue_pairs = xdp_qp;
                err = virtnet_reset(vi);
-               if (err)
+               if (err) {
+                       dev_warn(&dev->dev, "XDP reset failure.\n");
                        goto virtio_reset_err;
+               }
+               vi->xdp_queue_pairs = xdp_qp;

But xdp_queue_pairs is being used to detect if we should allocate the XDP
headroom. If we move it here do we have a set of buffers in the ring without
the proper headroom when we assign the xdp program below?

Right, so how about passing xdp_queue_pairs as a parameter to
virtnet_reset(). Then virtnet_reset() can set it after _remove_vq_common()
but before virtnet_restore_up()?

Thanks

Jason, wouldn't you say it's cleaner to avoid resets?
Would you be interested in completing this work:

20170207053455-mutt-send-email-...@kernel.org

Yes, but this seems still need drop packets, is this acceptable?

Thanks