2 files changed, 62 insertions, 13 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index e25b97062ce1..687ba8c9973d 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -58,15 +58,23 @@ struct completion;
  * be biten later when the calling function happens to sleep when it is not
  * supposed to.
  */
+#ifdef CONFIG_PREEMPT_VOLUNTARY
+extern int cond_resched(void);
+# define might_resched() cond_resched()
+#else
+# define might_resched() do { } while (0)
+#endif
+
 #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
-#define might_sleep() __might_sleep(__FILE__, __LINE__)
-#define might_sleep_if(cond) do { if (unlikely(cond)) might_sleep(); } while (0)
-void __might_sleep(char *file, int line);
+  void __might_sleep(char *file, int line);
+# define might_sleep() \
+        do { __might_sleep(__FILE__, __LINE__); might_resched(); } while (0)
 #else
-#define might_sleep() do {} while(0)
-#define might_sleep_if(cond) do {} while (0)
+# define might_sleep() do { might_resched(); } while (0)
 #endif
 
+#define might_sleep_if(cond) do { if (unlikely(cond)) might_sleep(); } while (0)
+
 #define abs(x) ({                               \
                 int __x = (x);                  \
                 (__x < 0) ? -__x : __x;         \
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 34c631221aa3..0b46a5dff4c0 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -1,15 +1,56 @@
 
-config PREEMPT
-        bool "Preemptible Kernel"
+choice
+        prompt "Preemption Model"
+        default PREEMPT_NONE
+
+config PREEMPT_NONE
+        bool "No Forced Preemption (Server)"
+        help
+          This is the traditional Linux preemption model, geared towards
+          throughput. It will still provide good latencies most of the
+          time, but there are no guarantees and occasional longer delays
+          are possible.
+
+          Select this option if you are building a kernel for a server or
+          scientific/computation system, or if you want to maximize the
+          raw processing power of the kernel, irrespective of scheduling
+          latencies.
+
+config PREEMPT_VOLUNTARY
+        bool "Voluntary Kernel Preemption (Desktop)"
         help
-          This option reduces the latency of the kernel when reacting to
-          real-time or interactive events by allowing a low priority process to
-          be preempted even if it is in kernel mode executing a system call.
-          This allows applications to run more reliably even when the system is
+          This option reduces the latency of the kernel by adding more
+          "explicit preemption points" to the kernel code. These new
+          preemption points have been selected to reduce the maximum
+          latency of rescheduling, providing faster application reactions,
+          at the cost of slighly lower throughput.
+
+          This allows reaction to interactive events by allowing a
+          low priority process to voluntarily preempt itself even if it
+          is in kernel mode executing a system call. This allows
+          applications to run more 'smoothly' even when the system is
           under load.
 
-          Say Y here if you are building a kernel for a desktop, embedded
-          or real-time system.  Say N if you are unsure.
+          Select this if you are building a kernel for a desktop system.
+
+config PREEMPT
+        bool "Preemptible Kernel (Low-Latency Desktop)"
+        help
+          This option reduces the latency of the kernel by making
+          all kernel code (that is not executing in a critical section)
+          preemptible.  This allows reaction to interactive events by
+          permitting a low priority process to be preempted involuntarily
+          even if it is in kernel mode executing a system call and would
+          otherwise not be about to reach a natural preemption point.
+          This allows applications to run more 'smoothly' even when the
+          system is under load, at the cost of slighly lower throughput
+          and a slight runtime overhead to kernel code.
+
+          Select this if you are building a kernel for a desktop or
+          embedded system with latency requirements in the milliseconds
+          range.
+
+endchoice
 
 config PREEMPT_BKL
         bool "Preempt The Big Kernel Lock"