Commit 2a3a041c authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by David S. Miller
Browse files

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



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: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0c54b85f

include/linux/tcp.h

+1 −0
Original line number Diff line number Diff line
@@ -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

net/ipv4/tcp.c

+12 −2
Original line number Diff line number Diff line
@@ -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;

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