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authorYuchung Cheng <ycheng@google.com>2017-10-04 22:59:59 +0300
committerDavid S. Miller <davem@davemloft.net>2017-10-06 07:24:47 +0300
commit043b87d7599ed8e86a33f4cbc3f062d57e263711 (patch)
tree349714731b8aab5ab172b8c199c0f084ff54dc53
parente2080072ed2d98a55ae69d95dea60ff7a17cddd5 (diff)
downloadlinux-043b87d7599ed8e86a33f4cbc3f062d57e263711.tar.xz
tcp: more efficient RACK loss detection
Use the new time-ordered list to speed up RACK. The detection logic is identical. But since the list is chronologically ordered by skb_mstamp and contains only skbs not yet acked or sacked, RACK can abort the loop upon hitting skbs that were sent more recently. On YouTube servers this patch reduces the iterations on write queue by 40x. The improvement is even bigger with large BDP networks. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/ipv4/tcp_recovery.c20
1 files changed, 5 insertions, 15 deletions
diff --git a/net/ipv4/tcp_recovery.c b/net/ipv4/tcp_recovery.c
index 449cd914d58e..8aa56caefde8 100644
--- a/net/ipv4/tcp_recovery.c
+++ b/net/ipv4/tcp_recovery.c
@@ -45,7 +45,7 @@ static bool tcp_rack_sent_after(u64 t1, u64 t2, u32 seq1, u32 seq2)
static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout)
{
struct tcp_sock *tp = tcp_sk(sk);
- struct sk_buff *skb;
+ struct sk_buff *skb, *n;
u32 reo_wnd;
*reo_timeout = 0;
@@ -58,17 +58,10 @@ static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout)
if ((tp->rack.reord || !tp->lost_out) && tcp_min_rtt(tp) != ~0U)
reo_wnd = max(tcp_min_rtt(tp) >> 2, reo_wnd);
- tcp_for_write_queue(skb, sk) {
+ list_for_each_entry_safe(skb, n, &tp->tsorted_sent_queue,
+ tcp_tsorted_anchor) {
struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
- if (skb == tcp_send_head(sk))
- break;
-
- /* Skip ones already (s)acked */
- if (!after(scb->end_seq, tp->snd_una) ||
- scb->sacked & TCPCB_SACKED_ACKED)
- continue;
-
if (tcp_rack_sent_after(tp->rack.mstamp, skb->skb_mstamp,
tp->rack.end_seq, scb->end_seq)) {
/* Step 3 in draft-cheng-tcpm-rack-00.txt:
@@ -81,6 +74,7 @@ static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout)
if (remaining < 0) {
tcp_rack_mark_skb_lost(sk, skb);
+ list_del_init(&skb->tcp_tsorted_anchor);
continue;
}
@@ -91,11 +85,7 @@ static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout)
/* Record maximum wait time (+1 to avoid 0) */
*reo_timeout = max_t(u32, *reo_timeout, 1 + remaining);
-
- } else if (!(scb->sacked & TCPCB_RETRANS)) {
- /* Original data are sent sequentially so stop early
- * b/c the rest are all sent after rack_sent
- */
+ } else {
break;
}
}