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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>
This commit is contained in:
Soheil Hassas Yeganeh 2016-04-27 23:39:01 -04:00 committed by David S. Miller
parent 863c1fd981
commit 0a2cf20c3f
5 changed files with 16 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/skbuff.h
View File

@ -382,14 +382,10 @@ enum {
/* generate software time stamp when entering packet scheduling */
SKBTX_SCHED_TSTAMP = 1 << 6,
/* generate software timestamp on peer data acknowledgment */
SKBTX_ACK_TSTAMP = 1 << 7,
};
#define SKBTX_ANY_SW_TSTAMP (SKBTX_SW_TSTAMP | \
SKBTX_SCHED_TSTAMP | \
SKBTX_ACK_TSTAMP)
SKBTX_SCHED_TSTAMP)
#define SKBTX_ANY_TSTAMP (SKBTX_HW_TSTAMP | SKBTX_ANY_SW_TSTAMP)
/*

5
net/ipv4/tcp.c
View File

@ -435,9 +435,10 @@ static void tcp_tx_timestamp(struct sock *sk, u16 tsflags, struct sk_buff *skb)
struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
sock_tx_timestamp(sk, tsflags, &shinfo->tx_flags);
if (shinfo->tx_flags & SKBTX_ANY_TSTAMP)
if (tsflags & SOF_TIMESTAMPING_TX_ACK)
tcb->txstamp_ack = 1;
if (tsflags & SOF_TIMESTAMPING_TX_RECORD_MASK)
shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
tcb->txstamp_ack = !!(shinfo->tx_flags & SKBTX_ACK_TSTAMP);
}
}

3
net/ipv4/tcp_input.c
View File

@ -3087,8 +3087,7 @@ static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
return;
shinfo = skb_shinfo(skb);
if ((shinfo->tx_flags & SKBTX_ACK_TSTAMP) &&
!before(shinfo->tskey, prior_snd_una) &&
if (!before(shinfo->tskey, prior_snd_una) &&
before(shinfo->tskey, tcp_sk(sk)->snd_una))
__skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
}

17
net/ipv4/tcp_output.c
View File

@ -1111,11 +1111,17 @@ static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int de
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 @@ u32 __tcp_select_window(struct sock *sk)
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;

3
net/socket.c
View File

@ -600,9 +600,6 @@ void __sock_tx_timestamp(__u16 tsflags, __u8 *tx_flags)
if (tsflags & SOF_TIMESTAMPING_TX_SCHED)
flags |= SKBTX_SCHED_TSTAMP;
if (tsflags & SOF_TIMESTAMPING_TX_ACK)
flags |= SKBTX_ACK_TSTAMP;
*tx_flags = flags;
}
EXPORT_SYMBOL(__sock_tx_timestamp);