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tcp: cache result of earlier divides when mss-aligning things

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The results is very unlikely change every so often so we
hardly need to divide again after doing that once for a
connection. Yet, if divide still becomes necessary we
detect that and do the right thing and again settle for
non-divide state. Takes the u16 space which was previously
taken by the plain xmit_size_goal.

This should take care part of the tso vs non-tso difference
we found earlier.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Ilpo Järvinen 2009-03-14 22:45:16 +00:00 committed by David S. Miller
parent 0c54b85f28
commit 2a3a041c4e
2 changed files with 13 additions and 2 deletions
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1
include/linux/tcp.h
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@ -248,6 +248,7 @@ struct tcp_sock {
/* inet_connection_sock has to be the first member of tcp_sock */
struct inet_connection_sock inet_conn;
u16 tcp_header_len; /* Bytes of tcp header to send */
u16 xmit_size_goal_segs; /* Goal for segmenting output packets */
/*
* Header prediction flags

14
net/ipv4/tcp.c
View file

@ -665,7 +665,7 @@ static unsigned int tcp_xmit_size_goal(struct sock *sk, u32 mss_now,
int large_allowed)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 xmit_size_goal;
u32 xmit_size_goal, old_size_goal;
xmit_size_goal = mss_now;
@ -676,7 +676,17 @@ static unsigned int tcp_xmit_size_goal(struct sock *sk, u32 mss_now,
tp->tcp_header_len);
xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal);
xmit_size_goal -= (xmit_size_goal % mss_now);
/* We try hard to avoid divides here */
old_size_goal = tp->xmit_size_goal_segs * mss_now;
if (likely(old_size_goal <= xmit_size_goal &&
old_size_goal + mss_now > xmit_size_goal)) {
xmit_size_goal = old_size_goal;
} else {
tp->xmit_size_goal_segs = xmit_size_goal / mss_now;
xmit_size_goal = tp->xmit_size_goal_segs * mss_now;
}
}
return xmit_size_goal;