tipc: improve poll() for group member socket

The current criteria for returning POLLOUT from a group member socket is
too simplistic. It basically returns POLLOUT as soon as the group has
external destinations, something obviously leading to a lot of spinning
during destination congestion situations. At the same time, the internal
congestion handling is unnecessarily complex.

We now change this as follows.

- We introduce an 'open' flag in  struct tipc_group. This flag is used
  only to help poll() get the setting of POLLOUT right, and *not* for
  congeston handling as such. This means that a user can choose to
  ignore an  EAGAIN for a destination and go on sending messages to
  other destinations in the group if he wants to.

- The flag is set to false every time we return EAGAIN on a send call.

- The flag is set to true every time any member, i.e., not necessarily
  the member that caused EAGAIN, is removed from the small_win list.

- We remove the group member 'usr_pending' flag. The size of the send
  window and presence in the 'small_win' list is sufficient criteria
  for recognizing congestion.

This solution seems to be a reasonable compromise between 'anycast',
which is normally not waiting for POLLOUT for a specific destination,
and the other three send modes, which are.

Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/tipc/group.h b/net/tipc/group.h
index dee7947..f4a596e 100644
--- a/net/tipc/group.h
+++ b/net/tipc/group.h
@@ -67,9 +67,9 @@ void tipc_group_update_bc_members(struct tipc_group *grp, int len, bool ack);
 bool tipc_group_cong(struct tipc_group *grp, u32 dnode, u32 dport,
 		     int len, struct tipc_member **m);
 bool tipc_group_bc_cong(struct tipc_group *grp, int len);
+bool tipc_group_is_open(struct tipc_group *grp);
 void tipc_group_update_rcv_win(struct tipc_group *grp, int blks, u32 node,
 			       u32 port, struct sk_buff_head *xmitq);
 u16 tipc_group_bc_snd_nxt(struct tipc_group *grp);
 void tipc_group_update_member(struct tipc_member *m, int len);
-int tipc_group_size(struct tipc_group *grp);
 #endif