Reverse the logic for ADAPTIVE_SX option and enable it by default.

Introduce for this operation the reverse NO_ADAPTIVE_SX option.
The flag SX_ADAPTIVESPIN to be passed to sx_init_flags(9) gets suppressed
and the new flag, offering the reversed logic, SX_NOADAPTIVE is added.

Additively implements adaptive spininning for sx held in shared mode.
The spinning limit can be handled through sysctls in order to be tuned
while the code doesn't reach the release, after which time they should
be dropped probabilly.

This change has made been necessary by recent benchmarks where it does
improve concurrency of workloads in presence of high contention
(ie. ZFS).

KPI breakage is documented by __FreeBSD_version bumping, manpage and
UPDATING updates.

Requested by:	jeff, kmacy
Reviewed by:	jeff
Tested by:	pho

1 files changed, 5 insertions, 5 deletions

diff --git a/share/man/man9/sx.9 b/share/man/man9/sx.9
index 41a7faa..c75c6a7 100644
--- a/share/man/man9/sx.9
+++ b/share/man/man9/sx.9
@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 25, 2007
+.Dd May 28, 2009
 .Dt SX 9
 .Os
 .Sh NAME
@@ -122,10 +122,10 @@ argument to
 specifies a set of optional flags to alter the behavior of
 .Fa sx .
 It contains one or more of the following flags:
-.Bl -tag -width SX_ADAPTIVESPIN
-.It Dv SX_ADAPTIVESPIN
-If the kernel is compiled with
-.Cd "options ADAPTIVE_SX" ,
+.Bl -tag -width SX_NOADAPTIVE
+.It Dv SX_NOADAPTIVE
+If the kernel is not compiled with
+.Cd "options NO_ADAPTIVE_SX" ,
 then lock operations for
 .Fa sx
 will spin instead of sleeping while an exclusive lock holder is executing on