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Subject[(RT RFC) PATCH v2 6/9] add a loop counter based timeout mechanism
Date
From: Sven Dietrich <sdietrich@novell.com>

Signed-off-by: Sven Dietrich <sdietrich@novell.com>
---
kernel/Kconfig.preempt | 11 +++++++++++
kernel/rtmutex.c | 4 ++++
kernel/rtmutex_adaptive.h | 11 +++++++++--
kernel/sysctl.c | 12 ++++++++++++
4 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index d2432fa..ac1cbad 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -203,6 +203,17 @@ config ADAPTIVE_RTLOCK

If unsure, say Y.

+config RTLOCK_DELAY
+ int "Default delay (in loops) for adaptive rtlocks"
+ range 0 1000000000
+ depends on ADAPTIVE_RTLOCK
+ default "10000"
+ help
+ This allows you to specify the maximum attempts a task will spin
+ attempting to acquire an rtlock before sleeping. The value is
+ tunable at runtime via a sysctl. A setting of 0 (zero) disables
+ the adaptive algorithm entirely.
+
config SPINLOCK_BKL
bool "Old-Style Big Kernel Lock"
depends on (PREEMPT || SMP) && !PREEMPT_RT
diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index 3802ef8..4a16b13 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -25,6 +25,10 @@
int rtmutex_lateral_steal __read_mostly = 1;
#endif

+#ifdef CONFIG_ADAPTIVE_RTLOCK
+int rtlock_timeout __read_mostly = CONFIG_RTLOCK_DELAY;
+#endif
+
/*
* lock->owner state tracking:
*
diff --git a/kernel/rtmutex_adaptive.h b/kernel/rtmutex_adaptive.h
index 862c088..60c6328 100644
--- a/kernel/rtmutex_adaptive.h
+++ b/kernel/rtmutex_adaptive.h
@@ -43,6 +43,7 @@
#ifdef CONFIG_ADAPTIVE_RTLOCK
struct adaptive_waiter {
struct task_struct *owner;
+ int timeout;
};

/*
@@ -64,7 +65,7 @@ adaptive_wait(struct rt_mutex *lock, struct rt_mutex_waiter *waiter,
{
int sleep = 0;

- for (;;) {
+ for (; adaptive->timeout > 0; adaptive->timeout--) {
/*
* If the task was re-awoken, break out completely so we can
* reloop through the lock-acquisition code.
@@ -105,6 +106,9 @@ adaptive_wait(struct rt_mutex *lock, struct rt_mutex_waiter *waiter,
cpu_relax();
}

+ if (adaptive->timeout <= 0)
+ sleep = 1;
+
put_task_struct(adaptive->owner);

return sleep;
@@ -122,8 +126,11 @@ prepare_adaptive_wait(struct rt_mutex *lock, struct adaptive_waiter *adaptive)
get_task_struct(adaptive->owner);
}

+extern int rtlock_timeout;
+
#define DECLARE_ADAPTIVE_WAITER(name) \
- struct adaptive_waiter name = { .owner = NULL, }
+ struct adaptive_waiter name = { .owner = NULL, \
+ .timeout = rtlock_timeout, }

#else

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c24c53d..55189ea 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -56,6 +56,8 @@
#include <asm/stacktrace.h>
#endif

+#include "rtmutex_adaptive.h"
+
static int deprecated_sysctl_warning(struct __sysctl_args *args);

#if defined(CONFIG_SYSCTL)
@@ -850,6 +852,16 @@ static struct ctl_table kern_table[] = {
.proc_handler = &proc_dointvec,
},
#endif
+#ifdef CONFIG_ADAPTIVE_RTLOCK
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "rtlock_timeout",
+ .data = &rtlock_timeout,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
+#endif
#ifdef CONFIG_PROC_FS
{
.ctl_name = CTL_UNNUMBERED,


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