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-rw-r--r--include/linux/kernel.h18
-rw-r--r--kernel/Kconfig.preempt57
2 files changed, 62 insertions, 13 deletions
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index e25b970..687ba8c 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 34c6312..0b46a5d 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"
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