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, 0 insertions, 12 deletions

diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 64fe8d5c067a..740d8a922e48 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -250,18 +250,6 @@ config KERNEL_STACK_ORDER
           be 1 << order pages.  The default is OK unless you're running Valgrind
           on UML, in which case, set this to 3.
 
-config UML_REAL_TIME_CLOCK
-        bool "Real-time Clock"
-        default y
-        help
-          This option makes UML time deltas match wall clock deltas.  This
-          should normally be enabled.  The exception would be if you are
-          debugging with UML and spend long times with UML stopped at a
-          breakpoint.  In this case, when UML is restarted, it will call the
-          timer enough times to make up for the time spent at the breakpoint.
-          This could result in a noticeable lag.  If this is a problem, then
-          disable this option.
-
 endmenu
 
 source "init/Kconfig"