uml: eliminate interrupts in the idle loop

Now, the idle loop now longer needs SIGALRM firing - it can just sleep for the
requisite amount of time and fake a timer interrupt when it finishes.

Any use of ITIMER_REAL now goes away.  disable_timer only turns off
ITIMER_VIRTUAL.  switch_timers is no longer needed, so it, and all calls, goes
away.

disable_timer now returns the amount of time remaining on the timer.
default_idle uses this to tell idle_sleep how long to sleep.  idle_sleep will
call alarm_handler if nanosleep returns 0, which is the case if it didn't
return early due to an interrupt.  Otherwise, it just returns.

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, 4 insertions, 3 deletions

diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index aef494b..0eae00b 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -235,6 +235,8 @@ void initial_thread_cb(void (*proc)(void *), void *arg)
 
 void default_idle(void)
 {
+	unsigned long long nsecs;
+
 	while(1) {
 		/* endless idle loop with no priority at all */
 
@@ -246,9 +248,8 @@ void default_idle(void)
 			schedule();
 
 		tick_nohz_stop_sched_tick();
-		switch_timers(1);
-		idle_sleep(10);
-		switch_timers(0);
+		nsecs = disable_timer();
+		idle_sleep(nsecs);
 		tick_nohz_restart_sched_tick();
 	}
 }