sfc: fallback for lack of xdp tx queues

If there are not enough resources to allocate one TX queue per core for
XDP TX it was completely disabled.

This patch implements a fallback solution for sharing the available
queues using __netif_tx_lock for synchronization. In the normal case that
there is one TX queue per CPU, no locking is done, as it was before.

With this fallback solution, XDP TX will work in much more cases that
were failing, specially in machines with many CPUs. It's hard for XDP
users to know what features are supported across different NICs and
configurations, so they will benefit on having wider support.

Signed-off-by: Íñigo Huguet <ihuguet@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 43 insertions, 11 deletions

diff --git a/drivers/net/ethernet/sfc/efx_channels.c b/drivers/net/ethernet/sfc/efx_channels.c
index e5b0d795c301..e7849f1260a1 100644
--- a/drivers/net/ethernet/sfc/efx_channels.c
+++ b/drivers/net/ethernet/sfc/efx_channels.c
@@ -166,32 +166,46 @@ static int efx_allocate_msix_channels(struct efx_nic *efx,
 	 * We need a channel per event queue, plus a VI per tx queue.
 	 * This may be more pessimistic than it needs to be.
 	 */
-	if (n_channels + n_xdp_ev > max_channels) {
+	if (n_channels >= max_channels) {
+		efx->xdp_txq_queues_mode = EFX_XDP_TX_QUEUES_DISABLED;
 		netif_err(efx, drv, efx->net_dev,
 			  "Insufficient resources for %d XDP event queues (%d other channels, max %d)\n",
 			  n_xdp_ev, n_channels, max_channels);
 		netif_err(efx, drv, efx->net_dev,
-			  "XDP_TX and XDP_REDIRECT will not work on this interface");
-		efx->n_xdp_channels = 0;
-		efx->xdp_tx_per_channel = 0;
-		efx->xdp_tx_queue_count = 0;
+			  "XDP_TX and XDP_REDIRECT will not work on this interface\n");
 	} else if (n_channels + n_xdp_tx > efx->max_vis) {
+		efx->xdp_txq_queues_mode = EFX_XDP_TX_QUEUES_DISABLED;
 		netif_err(efx, drv, efx->net_dev,
 			  "Insufficient resources for %d XDP TX queues (%d other channels, max VIs %d)\n",
 			  n_xdp_tx, n_channels, efx->max_vis);
 		netif_err(efx, drv, efx->net_dev,
-			  "XDP_TX and XDP_REDIRECT will not work on this interface");
-		efx->n_xdp_channels = 0;
-		efx->xdp_tx_per_channel = 0;
-		efx->xdp_tx_queue_count = 0;
+			  "XDP_TX and XDP_REDIRECT will not work on this interface\n");
+	} else if (n_channels + n_xdp_ev > max_channels) {
+		efx->xdp_txq_queues_mode = EFX_XDP_TX_QUEUES_SHARED;
+		netif_warn(efx, drv, efx->net_dev,
+			   "Insufficient resources for %d XDP event queues (%d other channels, max %d)\n",
+			   n_xdp_ev, n_channels, max_channels);
+
+		n_xdp_ev = max_channels - n_channels;
+		netif_warn(efx, drv, efx->net_dev,
+			   "XDP_TX and XDP_REDIRECT will work with reduced performance (%d cpus/tx_queue)\n",
+			   DIV_ROUND_UP(n_xdp_tx, tx_per_ev * n_xdp_ev));
 	} else {
+		efx->xdp_txq_queues_mode = EFX_XDP_TX_QUEUES_DEDICATED;
+	}
+
+	if (efx->xdp_txq_queues_mode != EFX_XDP_TX_QUEUES_DISABLED) {
 		efx->n_xdp_channels = n_xdp_ev;
 		efx->xdp_tx_per_channel = tx_per_ev;
 		efx->xdp_tx_queue_count = n_xdp_tx;
 		n_channels += n_xdp_ev;
 		netif_dbg(efx, drv, efx->net_dev,
 			  "Allocating %d TX and %d event queues for XDP\n",
-			  n_xdp_tx, n_xdp_ev);
+			  n_xdp_ev * tx_per_ev, n_xdp_ev);
+	} else {
+		efx->n_xdp_channels = 0;
+		efx->xdp_tx_per_channel = 0;
+		efx->xdp_tx_queue_count = 0;
 	}
 
 	if (vec_count < n_channels) {
@@ -921,7 +935,25 @@ int efx_set_channels(struct efx_nic *efx)
 			}
 		}
 	}
-	WARN_ON(xdp_queue_number != efx->xdp_tx_queue_count);
+	WARN_ON(efx->xdp_txq_queues_mode == EFX_XDP_TX_QUEUES_DEDICATED &&
+		xdp_queue_number != efx->xdp_tx_queue_count);
+	WARN_ON(efx->xdp_txq_queues_mode != EFX_XDP_TX_QUEUES_DEDICATED &&
+		xdp_queue_number > efx->xdp_tx_queue_count);
+
+	/* If we have less XDP TX queues than CPUs, assign the already existing
+	 * queues to the exceeding CPUs (this means that we will have to use
+	 * locking when transmitting with XDP)
+	 */
+	next_queue = 0;
+	while (xdp_queue_number < efx->xdp_tx_queue_count) {
+		tx_queue = efx->xdp_tx_queues[next_queue++];
+		channel = tx_queue->channel;
+		netif_dbg(efx, drv, efx->net_dev, "Channel %u TXQ %u is XDP %u, HW %u\n",
+			  channel->channel, tx_queue->label,
+			  xdp_queue_number, tx_queue->queue);
+
+		efx->xdp_tx_queues[xdp_queue_number++] = tx_queue;
+	}
 
 	rc = netif_set_real_num_tx_queues(efx->net_dev, efx->n_tx_channels);
 	if (rc)