[PATCH net-next 2/3] packet: don't unconditionally schedule() in case of MSG_DONTWAIT
From: Daniel Borkmann <hidden>
Date: 2014-01-12 16:22:55
Subsystem:
networking [general], packet sockets, the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Willem de Bruijn, Linus Torvalds
In tpacket_snd(), when we've discovered a first frame that is not in status TP_STATUS_SEND_REQUEST, and return a NULL buffer, we exit the send routine in case of MSG_DONTWAIT, since we've finished traversing the mmaped send ring buffer and don't care about pending frames. While doing so, we still unconditionally call an expensive schedule() in the packet_current_frame() "error" path, which is unnecessary in this case since it's enough to just quit the function. Also, in case MSG_DONTWAIT is not set, we should rather test for need_resched() first and do schedule() only if necessary since meanwhile pending frames could already have finished processing and called skb destructor. Signed-off-by: Daniel Borkmann <redacted> --- net/packet/af_packet.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-)
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 85bb38c..d5495d8 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c@@ -2156,6 +2156,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) int err, reserve = 0; void *ph; struct sockaddr_ll *saddr = (struct sockaddr_ll *)msg->msg_name; + bool need_wait = !(msg->msg_flags & MSG_DONTWAIT); int tp_len, size_max; unsigned char *addr; int len_sum = 0;
@@ -2198,10 +2199,10 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) do { ph = packet_current_frame(po, &po->tx_ring, - TP_STATUS_SEND_REQUEST); - + TP_STATUS_SEND_REQUEST); if (unlikely(ph == NULL)) { - schedule(); + if (need_wait && need_resched()) + schedule(); continue; }
@@ -2255,10 +2256,8 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) } packet_increment_head(&po->tx_ring); len_sum += tp_len; - } while (likely((ph != NULL) || - ((!(msg->msg_flags & MSG_DONTWAIT)) && - (atomic_read(&po->tx_ring.pending)))) - ); + } while (likely((ph != NULL) || (need_wait && + atomic_read(&po->tx_ring.pending)))); err = len_sum; goto out_put;
--
1.7.11.7