This patch introduces a cpu time clock for s390 (only ticking
if the virtual cpu is running) and bases the s390 implementation
of sched_clock() on it.
The times lice length on a virtual cpu can be anything
between the calculated time slice and zero. In reality
this doesn't seem to be problem, since the scheduler is fair
enough to not let a single process starve but the current
implementation can lead to inefficient short time slices.
By providing a 'virtual' sched_clock() we guarantee that a
process can get its time slice regardless of scheduling
decisions from the hypervisor.
Patch applies to 2.6.22 git and works fine with CFS.
Jan
--
arch/s390/kernel/time.c | 18 ++++++++++++------
arch/s390/kernel/vtime.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
include/asm-s390/timer.h | 2 ++
3 files changed, 59 insertions(+), 6 deletions(-)
--- ./include/asm-s390/timer.h.cpu_clock 2007-07-18 13:43:53.000000000
+0200
+++ ./include/asm-s390/timer.h 2007-07-18 20:41:13.000000000 +0200
@@ -48,6 +48,8 @@
extern void init_cpu_vtimer(void);
extern void vtime_init(void);
+extern unsigned long long cpu_clock(void);
+
#endif /* __KERNEL__ */
#endif /* _ASM_S390_TIMER_H */
--- ./arch/s390/kernel/time.c.cpu_clock 2007-07-18 13:43:35.000000000 +0200
+++ ./arch/s390/kernel/time.c 2007-07-18 21:01:07.000000000 +0200
@@ -62,21 +62,27 @@
static u64 xtime_cc;
/*
- * Scheduler clock - returns current time in nanosec units.
+ * Monotonic_clock - returns # of nanoseconds passed since time_init()
*/
-unsigned long long sched_clock(void)
+unsigned long long monotonic_clock(void)
{
return ((get_clock() - jiffies_timer_cc) * 125) >> 9;
}
+EXPORT_SYMBOL(monotonic_clock);
/*
- * Monotonic_clock - returns # of nanoseconds passed since time_init()
+ * Scheduler clock - returns current time in nanosec units.
+ * Now based on virtual cpu time to only account time the guest
+ * was actually running.
*/
-unsigned long long monotonic_clock(void)
+unsigned long long sched_clock(void)
{
- return sched_clock();
+#ifdef CONFIG_VIRT_TIMER
+ return cpu_clock();
+#else
+ return monotonic_clock();
+#endif
}
-EXPORT_SYMBOL(monotonic_clock);
void tod_to_timeval(__u64 todval, struct timespec *xtime)
{
--- ./arch/s390/kernel/vtime.c.cpu_clock 2007-07-18 13:43:44.000000000
+0200
+++ ./arch/s390/kernel/vtime.c 2007-07-18 20:52:14.000000000 +0200
@@ -26,6 +26,44 @@
static ext_int_info_t ext_int_info_timer;
static DEFINE_PER_CPU(struct vtimer_queue, virt_cpu_timer);
+static DEFINE_PER_CPU(struct vtimer_list, cpu_clock_timer);
+
+/*
+ * read the remaining time of a virtual timer running on the current cpu
+ */
+static unsigned long long read_cpu_timer(struct vtimer_list *timer)
+{
+ struct vtimer_queue *vt_list;
+ unsigned long flags;
+ __u64 done;
+
+ local_irq_save(flags);
+ local_irq_disable();
+
+ BUG_ON(timer->cpu != smp_processor_id());
+
+ vt_list = &per_cpu(virt_cpu_timer, timer->cpu);
+ asm volatile ("STPT %0" : "=m" (done));
+
+ done = vt_list->to_expire + vt_list->offset - done;
+ local_irq_restore(flags);
+ return done;
+}
+
+/*
+ * Cpu clock, returns cpu time in nanosec units.
+ * Must be called with preemption disabled.
+ */
+unsigned long long cpu_clock(void)
+{
+ return ((read_cpu_timer(&__get_cpu_var(cpu_clock_timer)) * 125) >> 9);
+}
+
+/* expire after 142 years ... */
+static void cpu_clock_timer_callback(unsigned long data)
+{
+ BUG();
+}
#ifdef CONFIG_VIRT_CPU_ACCOUNTING
/*
@@ -522,6 +560,7 @@
void init_cpu_vtimer(void)
{
struct vtimer_queue *vt_list;
+ struct vtimer_list *timer;
/* kick the virtual timer */
S390_lowcore.exit_timer = VTIMER_MAX_SLICE;
@@ -539,6 +578,12 @@
vt_list->offset = 0;
vt_list->idle = 0;
+ /* add dummy timers needed for cpu_clock */
+ timer = &__get_cpu_var(cpu_clock_timer);
+ init_virt_timer(timer);
+ timer->expires = VTIMER_MAX_SLICE;
+ timer->function = cpu_clock_timer_callback;
+ add_virt_timer(timer);
}
static int vtimer_idle_notify(struct notifier_block *self,
-
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