sched: high-res preemption tick

Use HR-timers (when available) to deliver an accurate preemption tick.

The regular scheduler tick that runs at 1/HZ can be too coarse when nice
level are used. The fairness system will still keep the cpu utilisation 'fair'
by then delaying the task that got an excessive amount of CPU time but try to
minimize this by delivering preemption points spot-on.

The average frequency of this extra interrupt is sched_latency / nr_latency.
Which need not be higher than 1/HZ, its just that the distribution within the
sched_latency period is important.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 7 insertions, 0 deletions

diff --git a/include/asm-x86/thread_info_32.h b/include/asm-x86/thread_info_32.h
index 22a8cbcd35e2..ef58fd2a6eb0 100644
--- a/include/asm-x86/thread_info_32.h
+++ b/include/asm-x86/thread_info_32.h
@@ -132,6 +132,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_SYSCALL_AUDIT       6       /* syscall auditing active */
 #define TIF_SECCOMP             7       /* secure computing */
 #define TIF_RESTORE_SIGMASK     8       /* restore signal mask in do_signal() */
+#define TIF_HRTICK_RESCHED      9       /* reprogram hrtick timer */
 #define TIF_MEMDIE              16
 #define TIF_DEBUG               17      /* uses debug registers */
 #define TIF_IO_BITMAP           18      /* uses I/O bitmap */
@@ -147,6 +148,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_SYSCALL_AUDIT      (1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP            (1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK    (1<<TIF_RESTORE_SIGMASK)
+#define _TIF_HRTICK_RESCHED     (1<<TIF_HRTICK_RESCHED)
 #define _TIF_DEBUG              (1<<TIF_DEBUG)
 #define _TIF_IO_BITMAP          (1<<TIF_IO_BITMAP)
 #define _TIF_FREEZE             (1<<TIF_FREEZE)
diff --git a/include/asm-x86/thread_info_64.h b/include/asm-x86/thread_info_64.h
index beae2bfb62ca..7f6ee68f0002 100644
--- a/include/asm-x86/thread_info_64.h
+++ b/include/asm-x86/thread_info_64.h
@@ -115,6 +115,7 @@ static inline struct thread_info *stack_thread_info(void)
 #define TIF_SECCOMP             8       /* secure computing */
 #define TIF_RESTORE_SIGMASK     9       /* restore signal mask in do_signal */
 #define TIF_MCE_NOTIFY          10      /* notify userspace of an MCE */
+#define TIF_HRTICK_RESCHED      11      /* reprogram hrtick timer */
 /* 16 free */
 #define TIF_IA32                17      /* 32bit process */ 
 #define TIF_FORK                18      /* ret_from_fork */
@@ -133,6 +134,7 @@ static inline struct thread_info *stack_thread_info(void)
 #define _TIF_SECCOMP            (1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK    (1<<TIF_RESTORE_SIGMASK)
 #define _TIF_MCE_NOTIFY         (1<<TIF_MCE_NOTIFY)
+#define _TIF_HRTICK_RESCHED     (1<<TIF_HRTICK_RESCHED)
 #define _TIF_IA32               (1<<TIF_IA32)
 #define _TIF_FORK               (1<<TIF_FORK)
 #define _TIF_ABI_PENDING        (1<<TIF_ABI_PENDING)
@@ -146,6 +148,9 @@ static inline struct thread_info *stack_thread_info(void)
 /* work to do on any return to user space */
 #define _TIF_ALLWORK_MASK (0x0000FFFF & ~_TIF_SECCOMP)
 
+#define _TIF_DO_NOTIFY_MASK \
+        (_TIF_SIGPENDING|_TIF_SINGLESTEP|_TIF_MCE_NOTIFY|_TIF_HRTICK_RESCHED)
+
 /* flags to check in __switch_to() */
 #define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP)