af_packet: don't pass empty blocks for PACKET_V3
Before da413eec729d ("packet: Fixed TPACKET V3 to signal poll when block is
closed rather than every packet") poll listening for an af_packet socket was
not signaled if there was no packets to process. After the patch poll is
signaled evety time when block retire timer expires. That happens because
af_packet closes the current block on timeout even if the block is empty.
Passing empty blocks to the user not only wastes CPU but also wastes ring
buffer space increasing probability of packets dropping on small timeouts.
Signed-off-by: Alexander Drozdov <al.drozdov@gmail.com>
Cc: Dan Collins <dan@dcollins.co.nz>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Guy Harris <guy@alum.mit.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 99fc628..5bf1e96 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -698,6 +698,10 @@
if (pkc->last_kactive_blk_num == pkc->kactive_blk_num) {
if (!frozen) {
+ if (!BLOCK_NUM_PKTS(pbd)) {
+ /* An empty block. Just refresh the timer. */
+ goto refresh_timer;
+ }
prb_retire_current_block(pkc, po, TP_STATUS_BLK_TMO);
if (!prb_dispatch_next_block(pkc, po))
goto refresh_timer;
@@ -798,7 +802,11 @@
h1->ts_last_pkt.ts_sec = last_pkt->tp_sec;
h1->ts_last_pkt.ts_nsec = last_pkt->tp_nsec;
} else {
- /* Ok, we tmo'd - so get the current time */
+ /* Ok, we tmo'd - so get the current time.
+ *
+ * It shouldn't really happen as we don't close empty
+ * blocks. See prb_retire_rx_blk_timer_expired().
+ */
struct timespec ts;
getnstimeofday(&ts);
h1->ts_last_pkt.ts_sec = ts.tv_sec;