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>
diff --git a/arch/um/include/os.h b/arch/um/include/os.h
index e4f2fe1..91642e4 100644
--- a/arch/um/include/os.h
+++ b/arch/um/include/os.h
@@ -251,11 +251,10 @@
/* time.c */
#define BILLION (1000 * 1000 * 1000)
-extern int switch_timers(int to_real);
-extern void idle_sleep(int secs);
+extern void idle_sleep(unsigned long long nsecs);
extern int set_interval(void);
extern int timer_one_shot(int ticks);
-extern void disable_timer(void);
+extern unsigned long long disable_timer(void);
extern void uml_idle_timer(void);
extern unsigned long long os_nsecs(void);
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 default_idle(void)
{
+ unsigned long long nsecs;
+
while(1) {
/* endless idle loop with no priority at all */
@@ -246,9 +248,8 @@
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();
}
}
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 53593c8..fbad174 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -120,7 +120,6 @@
void handle_signal(int sig, struct sigcontext *sc)
{
unsigned long pending = 1UL << sig;
- int timer = switch_timers(0);
do {
int nested, bail;
@@ -157,8 +156,6 @@
if (!nested)
pending = from_irq_stack(nested);
} while (pending);
-
- switch_timers(timer);
}
extern void hard_handler(int sig);
diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index 9ffc61a..d2cb161 100644
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -12,8 +12,6 @@
#include "os.h"
#include "user.h"
-static int is_real_timer = 0;
-
int set_interval(void)
{
int usec = 1000000/UM_HZ;
@@ -41,47 +39,15 @@
return 0;
}
-void disable_timer(void)
+unsigned long long disable_timer(void)
{
- struct itimerval disable = ((struct itimerval) { { 0, 0 }, { 0, 0 }});
+ struct itimerval time = ((struct itimerval) { { 0, 0 }, { 0, 0 } });
- if ((setitimer(ITIMER_VIRTUAL, &disable, NULL) < 0) ||
- (setitimer(ITIMER_REAL, &disable, NULL) < 0))
+ if(setitimer(ITIMER_VIRTUAL, &time, &time) < 0)
printk(UM_KERN_ERR "disable_timer - setitimer failed, "
"errno = %d\n", errno);
-}
-int switch_timers(int to_real)
-{
- struct itimerval disable = ((struct itimerval) { { 0, 0 }, { 0, 0 }});
- struct itimerval enable;
- int old, new, old_type = is_real_timer;
-
- if(to_real == old_type)
- return to_real;
-
- if (to_real) {
- old = ITIMER_VIRTUAL;
- new = ITIMER_REAL;
- }
- else {
- old = ITIMER_REAL;
- new = ITIMER_VIRTUAL;
- }
-
- if (setitimer(old, &disable, &enable) < 0)
- printk(UM_KERN_ERR "switch_timers - setitimer disable failed, "
- "errno = %d\n", errno);
-
- if((enable.it_value.tv_sec == 0) && (enable.it_value.tv_usec == 0))
- enable.it_value = enable.it_interval;
-
- if (setitimer(new, &enable, NULL))
- printk(UM_KERN_ERR "switch_timers - setitimer enable failed, "
- "errno = %d\n", errno);
-
- is_real_timer = to_real;
- return old_type;
+ return tv_to_nsec(&time.it_value);
}
unsigned long long os_nsecs(void)
@@ -92,11 +58,13 @@
return timeval_to_ns(&tv);
}
-void idle_sleep(int secs)
-{
- struct timespec ts;
+extern void alarm_handler(int sig, struct sigcontext *sc);
- ts.tv_sec = secs;
- ts.tv_nsec = 0;
- nanosleep(&ts, NULL);
+void idle_sleep(unsigned long long nsecs)
+{
+ struct timespec ts = { .tv_sec = nsecs / BILLION,
+ .tv_nsec = nsecs % BILLION };
+
+ if (nanosleep(&ts, &ts) == 0)
+ alarm_handler(SIGVTALRM, NULL);
}