Merge branch 'ndo_xdp_xmit-cleanup'

Jesper Dangaard Brouer says:

====================
As I mentioned in merge commit 10f678683e4 ("Merge branch 'xdp_xmit-bulking'")
I plan to change the API for ndo_xdp_xmit once more, by adding a flags
argument, which is done in this patchset.

I know it is late in the cycle (currently at rc7), but it would be
nice to avoid changing NDOs over several kernel releases, as it is
annoying to vendors and distro backporters, but it is not strictly
UAPI so it is allowed (according to Alexei).

The end-goal is getting rid of the ndo_xdp_flush operation, as it will
make it possible for drivers to implement a TXQ synchronization mechanism
that is not necessarily derived from the CPU id (smp_processor_id).

This patchset removes all callers of the ndo_xdp_flush operation, but
it doesn't take the last step of removing it from all drivers.  This
can be done later, or I can update the patchset on request.

Micro-benchmarks only show a very small performance improvement, for
map-redirect around ~2 ns, and for non-map redirect ~7 ns.  I've not
benchmarked this with CONFIG_RETPOLINE, but the performance benefit
should be more visible given we end-up removing an indirect call.

---
V2: Updated based on feedback from Song Liu <songliubraving@fb.com>
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 8 insertions, 3 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 8452f72087ef..7f17785a59d7 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1185,13 +1185,13 @@ struct dev_ifalias {
  *	This function is used to set or query state related to XDP on the
  *	netdevice and manage BPF offload. See definition of
  *	enum bpf_netdev_command for details.
- * int (*ndo_xdp_xmit)(struct net_device *dev, int n, struct xdp_frame **xdp);
+ * int (*ndo_xdp_xmit)(struct net_device *dev, int n, struct xdp_frame **xdp,
+ *			u32 flags);
  *	This function is used to submit @n XDP packets for transmit on a
  *	netdevice. Returns number of frames successfully transmitted, frames
  *	that got dropped are freed/returned via xdp_return_frame().
  *	Returns negative number, means general error invoking ndo, meaning
  *	no frames were xmit'ed and core-caller will free all frames.
- *	TODO: Consider add flag to allow sending flush operation.
  * void (*ndo_xdp_flush)(struct net_device *dev);
  *	This function is used to inform the driver to flush a particular
  *	xdp tx queue. Must be called on same CPU as xdp_xmit.
@@ -1380,7 +1380,8 @@ struct net_device_ops {
 	int			(*ndo_bpf)(struct net_device *dev,
 					   struct netdev_bpf *bpf);
 	int			(*ndo_xdp_xmit)(struct net_device *dev, int n,
-						struct xdp_frame **xdp);
+						struct xdp_frame **xdp,
+						u32 flags);
 	void			(*ndo_xdp_flush)(struct net_device *dev);
 };
 
diff --git a/include/net/xdp.h b/include/net/xdp.h
index 7ad779237ae8..a3b71a4dd71d 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -40,6 +40,10 @@ enum xdp_mem_type {
 	MEM_TYPE_MAX,
 };
 
+/* XDP flags for ndo_xdp_xmit */
+#define XDP_XMIT_FLUSH		(1U << 0)	/* doorbell signal consumer */
+#define XDP_XMIT_FLAGS_MASK	XDP_XMIT_FLUSH
+
 struct xdp_mem_info {
 	u32 type; /* enum xdp_mem_type, but known size type */
 	u32 id;