Refactor select to reduce contention and hide internal implementation

details from consumers.

 - Track individual selecters on a per-descriptor basis such that there
   are no longer collisions and after sleeping for events only those
   descriptors which triggered events must be rescaned.
 - Protect the selinfo (per descriptor) structure with a mtx pool mutex.
   mtx pool mutexes were chosen to preserve api compatibility with
   existing code which does nothing but bzero() to setup selinfo
   structures.
 - Use a per-thread wait channel rather than a global wait channel.
 - Hide select implementation details in a seltd structure which is
   opaque to the rest of the kernel.
 - Provide a 'selsocket' interface for those kernel consumers who wish to
   select on a socket when they have no fd so they no longer have to
   be aware of select implementation details.

Tested by:	kris
Reviewed on:	arch

1 files changed, 2 insertions, 1 deletions

diff --git a/sys/kern/uipc_sockbuf.c b/sys/kern/uipc_sockbuf.c
index e1fc341..aa1d5ce 100644
--- a/sys/kern/uipc_sockbuf.c
+++ b/sys/kern/uipc_sockbuf.c
@@ -176,7 +176,8 @@ sowakeup(struct socket *so, struct sockbuf *sb)
 	SOCKBUF_LOCK_ASSERT(sb);
 
 	selwakeuppri(&sb->sb_sel, PSOCK);
-	sb->sb_flags &= ~SB_SEL;
+	if (!SEL_WAITING(&sb->sb_sel))
+		sb->sb_flags &= ~SB_SEL;
 	if (sb->sb_flags & SB_WAIT) {
 		sb->sb_flags &= ~SB_WAIT;
 		wakeup(&sb->sb_cc);