Refactor timer management code with priority to one-shot operation mode.

The main goal of this is to generate timer interrupts only when there is
some work to do. When CPU is busy interrupts are generating at full rate
of hz + stathz to fullfill scheduler and timekeeping requirements. But
when CPU is idle, only minimum set of interrupts (down to 8 interrupts per
second per CPU now), needed to handle scheduled callouts is executed.
This allows significantly increase idle CPU sleep time, increasing effect
of static power-saving technologies. Also it should reduce host CPU load
on virtualized systems, when guest system is idle.

There is set of tunables, also available as writable sysctls, allowing to
control wanted event timer subsystem behavior:
  kern.eventtimer.timer - allows to choose event timer hardware to use.
On x86 there is up to 4 different kinds of timers. Depending on whether
chosen timer is per-CPU, behavior of other options slightly differs.
  kern.eventtimer.periodic - allows to choose periodic and one-shot
operation mode. In periodic mode, current timer hardware taken as the only
source of time for time events. This mode is quite alike to previous kernel
behavior. One-shot mode instead uses currently selected time counter
hardware to schedule all needed events one by one and program timer to
generate interrupt exactly in specified time. Default value depends of
chosen timer capabilities, but one-shot mode is preferred, until other is
forced by user or hardware.
  kern.eventtimer.singlemul - in periodic mode specifies how much times
higher timer frequency should be, to not strictly alias hardclock() and
statclock() events. Default values are 2 and 4, but could be reduced to 1
if extra interrupts are unwanted.
  kern.eventtimer.idletick - makes each CPU to receive every timer interrupt
independently of whether they busy or not. By default this options is
disabled. If chosen timer is per-CPU and runs in periodic mode, this option
has no effect - all interrupts are generating.

As soon as this patch modifies cpu_idle() on some platforms, I have also
refactored one on x86. Now it makes use of MONITOR/MWAIT instrunctions
(if supported) under high sleep/wakeup rate, as fast alternative to other
methods. It allows SMP scheduler to wake up sleeping CPUs much faster
without using IPI, significantly increasing performance on some highly
task-switching loads.

Tested by:	many (on i386, amd64, sparc64 and powerc)
H/W donated by:	Gheorghe Ardelean
Sponsored by:	iXsystems, Inc.

4 files changed, 12 insertions, 14 deletions

diff --git a/sys/sun4v/include/intr_machdep.h b/sys/sun4v/include/intr_machdep.h
index 370a5c0..f686e66 100644
--- a/sys/sun4v/include/intr_machdep.h
+++ b/sys/sun4v/include/intr_machdep.h
@@ -47,7 +47,6 @@
 #define	PIL_STOP	5	/* stop cpu ipi */
 #define	PIL_PREEMPT	6	/* preempt idle thread cpu ipi */
 #define	PIL_HARDCLOCK	7	/* hardclock broadcast */
-#define	PIL_STATCLOCK	8	/* statclock broadcast */
 #define	PIL_FAST	13	/* fast interrupts */
 #define	PIL_TICK	14
 
diff --git a/sys/sun4v/include/smp.h b/sys/sun4v/include/smp.h
index 56c50eb..3202089 100644
--- a/sys/sun4v/include/smp.h
+++ b/sys/sun4v/include/smp.h
@@ -47,7 +47,6 @@
 #define	IPI_STOP_HARD	PIL_STOP
 #define IPI_PREEMPT     PIL_PREEMPT
 #define	IPI_HARDCLOCK	PIL_HARDCLOCK
-#define	IPI_STATCLOCK	PIL_STATCLOCK
 
 #define	IPI_RETRIES	5000
 
@@ -83,7 +82,6 @@ void cpu_ipi_ast(struct trapframe *tf);
 void cpu_ipi_stop(struct trapframe *tf);
 void cpu_ipi_preempt(struct trapframe *tf);
 void cpu_ipi_hardclock(struct trapframe *tf);
-void cpu_ipi_statclock(struct trapframe *tf);
 
 void	ipi_all_but_self(u_int ipi);
 void	ipi_cpu(int cpu, u_int ipi);
diff --git a/sys/sun4v/sun4v/intr_machdep.c b/sys/sun4v/sun4v/intr_machdep.c
index 123493e..3587402 100644
--- a/sys/sun4v/sun4v/intr_machdep.c
+++ b/sys/sun4v/sun4v/intr_machdep.c
@@ -110,8 +110,7 @@ static char *pil_names[] = {
 	"stop",		/* PIL_STOP */
 	"preempt",      /* PIL_PREEMPT */
 	"hardclock",	/* PIL_HARDCLOCK */
-	"statclock",	/* PIL_STATCLOCK */
-	"stray", "stray", "stray", "stray",
+	"stray", "stray", "stray", "stray", "stray",
 	"fast",		/* PIL_FAST */
 	"tick",		/* PIL_TICK */
 };
@@ -265,7 +264,6 @@ intr_init(void)
 	intr_handlers[PIL_STOP]= cpu_ipi_stop;
 	intr_handlers[PIL_PREEMPT]= cpu_ipi_preempt;
 	intr_handlers[PIL_HARDCLOCK]= cpu_ipi_hardclock;
-	intr_handlers[PIL_STATCLOCK]= cpu_ipi_statclock;
 #endif
 	mtx_init(&intr_table_lock, "intr table", NULL, MTX_SPIN);
 	cpu_intrq_alloc();
diff --git a/sys/sun4v/sun4v/mp_machdep.c b/sys/sun4v/sun4v/mp_machdep.c
index 2e9a378..a9535e3 100644
--- a/sys/sun4v/sun4v/mp_machdep.c
+++ b/sys/sun4v/sun4v/mp_machdep.c
@@ -472,15 +472,18 @@ cpu_ipi_preempt(struct trapframe *tf)
 void
 cpu_ipi_hardclock(struct trapframe *tf)
 {
+	struct trapframe *oldframe;
+	struct thread *td;
 
-	hardclockintr(tf);
-}
-
-void
-cpu_ipi_statclock(struct trapframe *tf)
-{
-
-	statclockintr(tf);
+	critical_enter();
+	td = curthread;
+	td->td_intr_nesting_level++;
+	oldframe = td->td_intr_frame;
+	td->td_intr_frame = tf;
+	hardclockintr();
+	td->td_intr_frame = oldframe;
+	td->td_intr_nesting_level--;
+	critical_exit();
 }
 
 void