Re: [RFC PATCH] virtio_net: XDP support for adjust_head

On 2017年01月04日 00:57, John Fastabend wrote:

quoted

quoted

quoted

+    /* 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.
+     */

We probably need reset the device here, but maybe Michale has more ideas. And if
we do this, another interesting thing to do is to disable EWMA and always use a
single page for each packet, this could almost eliminate linearizing.

Well with normal MTU 1500 size we should not hit the linearizing case right? The
question is should we cap the MTU at GOOD_PACKET_LEN vs the current cap of
(PAGE_SIZE - overhead).

Sorry responding to my own post with a bit more detail. I don't really like
going to a page for each packet because we end up with double the pages in use
for the "normal" 1500 MTU case. We could make the xdp allocation scheme smarter
and allocate a page per packet when MTU is greater than 2k instead of using the
EWMA but I would push those types of things at net-next and live with the
linearizing behavior for now or capping the MTU.

Yes, agree.

Thanks