uml: tickless support

Enable tickless support.

CONFIG_TICK_ONESHOT and CONFIG_NO_HZ are enabled.

itimer_clockevent gets CLOCK_EVT_FEAT_ONESHOT and an implementation of
.set_next_event.

CONFIG_UML_REAL_TIME_CLOCK goes away because it only makes sense when there is
a clock ticking away all the time.  timer_handler now just calls do_IRQ once
without trying to figure out how many ticks to emulate.

The idle loop now needs to turn ticking on and off.

Userspace ticks keep happening as usual.  However, the userspace loop keep
track of when the next wakeup should happen and suppresses process ticks until
that happens.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index 6ff3d98281ba..9ffc61ac8ed6 100644
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -26,6 +26,21 @@ int set_interval(void)
         return 0;
 }
 
+int timer_one_shot(int ticks)
+{
+        unsigned long usec = ticks * 1000000 / UM_HZ;
+        unsigned long sec = usec / 1000000;
+        struct itimerval interval;
+
+        usec %= 1000000;
+        interval = ((struct itimerval) { { 0, 0 }, { sec, usec } });
+
+        if (setitimer(ITIMER_VIRTUAL, &interval, NULL) == -1)
+                return -errno;
+
+        return 0;
+}
+
 void disable_timer(void)
 {
         struct itimerval disable = ((struct itimerval) { { 0, 0 }, { 0, 0 }});
@@ -74,7 +89,7 @@ unsigned long long os_nsecs(void)
         struct timeval tv;
 
         gettimeofday(&tv, NULL);
-        return (unsigned long long) tv.tv_sec * BILLION + tv.tv_usec * 1000;
+        return timeval_to_ns(&tv);
 }
 
 void idle_sleep(int secs)