[PATCH] s390: spin lock retry

Split spin lock and r/w lock implementation into a single try which is done
inline and an out of line function that repeatedly tries to get the lock
before doing the cpu_relax().  Add a system control to set the number of
retries before a cpu is yielded.

The reason for the spin lock retry is that the diagnose 0x44 that is used to
give up the virtual cpu is quite expensive.  For spin locks that are held only
for a short period of time the costs of the diagnoses outweights the savings
for spin locks that are held for a longer timer.  The default retry count is
1000.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 11 insertions, 1 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e60b9c36f1f0..3e0bbee549ea 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -114,6 +114,7 @@ extern int unaligned_enabled;
 extern int sysctl_ieee_emulation_warnings;
 #endif
 extern int sysctl_userprocess_debug;
+extern int spin_retry;
 #endif
 
 extern int sysctl_hz_timer;
@@ -647,7 +648,16 @@ static ctl_table kern_table[] = {
                 .mode           = 0644,
                 .proc_handler   = &proc_dointvec,
         },
-
+#if defined(CONFIG_ARCH_S390)
+        {
+                .ctl_name       = KERN_SPIN_RETRY,
+                .procname       = "spin_retry",
+                .data           = &spin_retry,
+                .maxlen         = sizeof (int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
+#endif
         { .ctl_name = 0 }
 };