can: mcp25xxfd: add prediction of CanFD frames sizes based on history

Allow prediction of can frame sizes based on the last 32 Can Frames
received.

Naive histogram approach hast been taken for now.

Some simple stats based on 1000 frames received with DLC=6:
==> /sys/kernel/debug/mcp25xxfd-spi0.0/can_fifo_rx/rx_reads_prefetched_too_few
16
==> /sys/kernel/debug/mcp25xxfd-spi0.0/can_fifo_rx/rx_reads_prefetched_too_few_bytes
96
==> /sys/kernel/debug/mcp25xxfd-spi0.0/can_fifo_rx/rx_reads_prefetched_too_many
0
==> /sys/kernel/debug/mcp25xxfd-spi0.0/can_fifo_rx/rx_reads_prefetched_too_many_bytes
0
==> /sys/kernel/debug/mcp25xxfd-spi0.0/can_fifo_rx/rx_reads_prefetch_predicted
6

The first 16 frames are predicted as 0, but after that the prediction is 6.

It should be possible to take this prediction to use bulk reads for CanFD
as well when we have a prediction of length of 48 or 64.

Signed-off-by: Martin Sperl <[email protected]>

Author: msperl

drivers/net/can/spi/mcp25xxfd/mcp25xxfd_can.h

@@ -640,6 +640,10 @@ struct mcp25xxfd_can_priv {
 		u64 rx_bulk_reads;
 #define RX_BULK_READ_STATS_BINS 8
 		u64 rx_bulk_read_sizes[RX_BULK_READ_STATS_BINS];
+#define RX_HISTORY_SIZE 32
+		u8 rx_history_dlc[RX_HISTORY_SIZE];
+		u8 rx_history_index;
+		u32 rx_reads_prefetch_predicted;
 	} stats;
 
 	/* bus state */

drivers/net/can/spi/mcp25xxfd/mcp25xxfd_can_rx.c

@@ -53,6 +53,8 @@ void mcp25xxfd_can_rx_fifo_debugfs(struct net_device *net)
 			   &cpriv->stats.rx_reads_prefetched_too_many);
 	debugfs_create_u64("rx_reads_prefetched_too_many_bytes", 0444, dir,
 			   &cpriv->stats.rx_reads_prefetched_too_many_bytes);
+	debugfs_create_u32("rx_reads_prefetch_predicted", 0444, dir,
+			   &cpriv->stats.rx_reads_prefetch_predicted);
 
 	/* present the fifos */
 	for (i = 0; i < RX_BULK_READ_STATS_BINS - 2; i++) {
@@ -73,6 +75,40 @@ void mcp25xxfd_can_rx_fifo_debugfs(struct net_device *net)
 }
 #endif
 
+static int mcp25xxfd_can_rx_predict_prefetch(struct net_device *net)
+{
+	struct mcp25xxfd_can_priv *cpriv = netdev_priv(net);
+	int dlc, i, highest;
+	u8 histo[16];
+
+	/* if we have a prfecth set then use that one */
+	if (rx_prefetch_bytes != -1)
+		return min_t(int, rx_prefetch_bytes,
+			     (net->mtu == CANFD_MTU) ? 64 : 8);
+
+	/* memset */
+	memset(histo, 0, sizeof(histo));
+
+	/* for all others compute the histogram */
+	for (i = 0; i < RX_HISTORY_SIZE; i++)
+		histo[cpriv->stats.rx_history_dlc[i]]++;
+
+	/* and now find the highest fit */
+	for (i = (net->mtu == CANFD_MTU) ? 15 : 8, dlc = 8, highest = 0;
+	      i >= 0; i--) {
+		if (highest < histo[i]) {
+			highest = histo[i];
+			dlc = i;
+		}
+	}
+
+	/* compute length from dlc */
+	cpriv->stats.rx_reads_prefetch_predicted = can_dlc2len(dlc);
+
+	/* return the predicted length */
+	return cpriv->stats.rx_reads_prefetch_predicted;
+}
+
 static
 struct sk_buff *mcp25xxfd_can_submit_rx_normal_frame(struct net_device *net,
 						     u32 id,
@@ -148,6 +184,12 @@ int mcp25xxfd_can_submit_rx_frame(struct spi_device *spi, int fifo)
 	if (rx->flags & CAN_OBJ_FLAGS_FDF)
 		cpriv->fifos.rx.fd_count++;
 
+	/* add to rx_dlc_history */
+	cpriv->stats.rx_history_dlc[cpriv->stats.rx_history_index] = dlc;
+	cpriv->stats.rx_history_index++;
+	if (cpriv->stats.rx_history_index >= RX_HISTORY_SIZE)
+		cpriv->stats.rx_history_index = 0;
+
 	/* allocate the skb buffer */
 	if (rx->flags & CAN_OBJ_FLAGS_FDF) {
 		flags = 0;
@@ -413,10 +455,7 @@ static int mcp25xxfd_can_read_rx_frames_fd(struct spi_device *spi)
 	int ret;
 
 	/* calculate optimal prefetch to use */
-	if (rx_prefetch_bytes != -1)
-		prefetch = min_t(int, rx_prefetch_bytes, 64);
-	else
-		prefetch = 8;
+	prefetch = mcp25xxfd_can_rx_predict_prefetch(net);
 
 	/* loop all frames */
 	for (i = 0, fifo = cpriv->fifos.rx.start;