tcp: remove SKBTX_ACK_TSTAMP since it is redundant
The SKBTX_ACK_TSTAMP flag is set in skb_shinfo->tx_flags when
the timestamp of the TCP acknowledgement should be reported on
error queue. Since accessing skb_shinfo is likely to incur a
cache-line miss at the time of receiving the ack, the
txstamp_ack bit was added in tcp_skb_cb, which is set iff
the SKBTX_ACK_TSTAMP flag is set for an skb. This makes
SKBTX_ACK_TSTAMP flag redundant.
Remove the SKBTX_ACK_TSTAMP and instead use the txstamp_ack bit
everywhere.
Note that this frees one bit in shinfo->tx_flags.
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Suggested-by: Willem de Bruijn <willemb@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index b1b2045..b3a31b4 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1111,11 +1111,17 @@
tcp_verify_left_out(tp);
}
+static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
+{
+ return TCP_SKB_CB(skb)->txstamp_ack ||
+ (skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
+}
+
static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
{
struct skb_shared_info *shinfo = skb_shinfo(skb);
- if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
+ if (unlikely(tcp_has_tx_tstamp(skb)) &&
!before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
@@ -2446,13 +2452,12 @@
void tcp_skb_collapse_tstamp(struct sk_buff *skb,
const struct sk_buff *next_skb)
{
- const struct skb_shared_info *next_shinfo = skb_shinfo(next_skb);
- u8 tsflags = next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
-
- if (unlikely(tsflags)) {
+ if (unlikely(tcp_has_tx_tstamp(next_skb))) {
+ const struct skb_shared_info *next_shinfo =
+ skb_shinfo(next_skb);
struct skb_shared_info *shinfo = skb_shinfo(skb);
- shinfo->tx_flags |= tsflags;
+ shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
shinfo->tskey = next_shinfo->tskey;
TCP_SKB_CB(skb)->txstamp_ack |=
TCP_SKB_CB(next_skb)->txstamp_ack;