[patch 07/28]xen: xen time implementation

Jeremy Fitzhardinge
2007-05-11T19:17:29Z

[-- Attachment #1: xen-time.patch --]
[-- Type: text/plain, Size: 11711 bytes --]

Time is implemented by using a clocksource which is driven from the
hypervisor's nanosecond timebase. Xen implements time by
extrapolating from known timestamps using the tsc; the hypervisor is
responsible for making sure that the tsc is constant rate and
synchronized between vcpus.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>

---
arch/i386/xen/Makefile | 2
arch/i386/xen/enlighten.c | 6
arch/i386/xen/time.c | 402 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 409 insertions(+), 1 deletion(-)

===================================================================
--- a/arch/i386/xen/Makefile
+++ b/arch/i386/xen/Makefile
@@ -1,2 +1,2 @@ obj-y := enlighten.o setup.o features.o
obj-y := enlighten.o setup.o features.o multicalls.o mmu.o \
- events.o
+ events.o time.o
===================================================================
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -595,6 +595,12 @@ static const struct paravirt_ops xen_par
.arch_setup = xen_arch_setup,
.init_IRQ = xen_init_IRQ,

+ .time_init = xen_time_init,
+ .set_wallclock = xen_set_wallclock,
+ .get_wallclock = xen_get_wallclock,
+ .get_cpu_khz = xen_cpu_khz,
+ .sched_clock = xen_clocksource_read,
+
.cpuid = xen_cpuid,

.set_debugreg = xen_set_debugreg,
===================================================================
--- /dev/null
+++ b/arch/i386/xen/time.c
@@ -0,0 +1,402 @@
+/*
+ * Xen time implementation.
+ *
+ * This is implemented in terms of a clocksource driver which uses
+ * the hypervisor clock as a nanosecond timebase, and a clockevent
+ * driver which uses the hypervisor's timer mechanism.
+ *
+ * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
+ */
+#include <linux/kernel.h>
+#include <linux/interrupt.h>
+#include <linux/clocksource.h>
+#include <linux/clockchips.h>
+
+#include <asm/xen/hypervisor.h>
+#include <asm/xen/hypercall.h>
+
+#include <xen/events.h>
+#include <xen/interface/xen.h>
+#include <xen/interface/vcpu.h>
+
+#include "xen-ops.h"
+
+#define XEN_SHIFT 22
+#define TIMER_SLOP 100000 /* Xen may fire a timer up to this many ns early */
+
+/* These are perodically updated in shared_info, and then copied here. */
+struct shadow_time_info {
+ u64 tsc_timestamp; /* TSC at last update of time vals. */
+ u64 system_timestamp; /* Time, in nanosecs, since boot. */
+ u32 tsc_to_nsec_mul;
+ int tsc_shift;
+ u32 version;
+};
+
+static DEFINE_PER_CPU(struct shadow_time_info, shadow_time);
+
+unsigned long xen_cpu_khz(void)
+{
+ u64 cpu_khz = 1000000ULL << 32;
+ const struct vcpu_time_info *info =
+ &HYPERVISOR_shared_info->vcpu_info[0].time;
+
+ do_div(cpu_khz, info->tsc_to_system_mul);
+ if (info->tsc_shift < 0)
+ cpu_khz <<= -info->tsc_shift;
+ else
+ cpu_khz >>= info->tsc_shift;
+
+ return cpu_khz;
+}
+
+/*
+ * Reads a consistent set of time-base values from Xen, into a shadow data
+ * area.
+ */
+static void get_time_values_from_xen(void)
+{
+ struct vcpu_time_info *src;
+ struct shadow_time_info *dst;
+
+ preempt_disable();
+
+ src = &__get_cpu_var(xen_vcpu)->time;
+ dst = &__get_cpu_var(shadow_time);
+
+ do {
+ dst->version = src->version;
+ rmb();
+ dst->tsc_timestamp = src->tsc_timestamp;
+ dst->system_timestamp = src->system_time;
+ dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
+ dst->tsc_shift = src->tsc_shift;
+ rmb();
+ } while ((src->version & 1) | (dst->version ^ src->version));
+
+ preempt_enable();
+}
+
+/*
+ * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
+ * yielding a 64-bit result.
+ */
+static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
+{
+ u64 product;
+#ifdef __i386__
+ u32 tmp1, tmp2;
+#endif
+
+ if (shift < 0)
+ delta >>= -shift;
+ else
+ delta <<= shift;
+
+#ifdef __i386__
+ __asm__ (
+ "mul %5 ; "
+ "mov %4,%%eax ; "
+ "mov %%edx,%4 ; "
+ "mul %5 ; "
+ "xor %5,%5 ; "
+ "add %4,%%eax ; "
+ "adc %5,%%edx ; "
+ : "=A" (product), "=r" (tmp1), "=r" (tmp2)
+ : "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
+#elif __x86_64__
+ __asm__ (
+ "mul %%rdx ; shrd $32,%%rdx,%%rax"
+ : "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
+#else
+#error implement me!
+#endif
+
+ return product;
+}
+
+static u64 get_nsec_offset(struct shadow_time_info *shadow)
+{
+ u64 now, delta;
+ rdtscll(now);
+ delta = now - shadow->tsc_timestamp;
+ return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
+}
+
+cycle_t xen_clocksource_read(void)
+{
+ struct shadow_time_info *shadow = &get_cpu_var(shadow_time);
+ cycle_t ret;
+
+ get_time_values_from_xen();
+
+ ret = shadow->system_timestamp + get_nsec_offset(shadow);
+
+ put_cpu_var(shadow_time);
+
+ return ret;
+}
+
+static void xen_read_wallclock(struct timespec *ts)
+{
+ const struct shared_info *s = HYPERVISOR_shared_info;
+ u32 version;
+ u64 delta;
+ struct timespec now;
+
+ /* get wallclock at system boot */
+ do {
+ version = s->wc_version;
+ rmb();
+ now.tv_sec = s->wc_sec;
+ now.tv_nsec = s->wc_nsec;
+ rmb();
+ } while ((s->wc_version & 1) | (version ^ s->wc_version));
+
+ delta = xen_clocksource_read(); /* time since system boot */
+ delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
+
+ now.tv_nsec = do_div(delta, NSEC_PER_SEC);
+ now.tv_sec = delta;
+
+ set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
+}
+
+unsigned long xen_get_wallclock(void)
+{
+ struct timespec ts;
+
+ xen_read_wallclock(&ts);
+
+ return ts.tv_sec;
+}
+
+int xen_set_wallclock(unsigned long now)
+{
+ /* do nothing for domU */
+ return -1;
+}
+
+static struct clocksource xen_clocksource __read_mostly = {
+ .name = "xen",
+ .rating = 400,
+ .read = xen_clocksource_read,
+ .mask = ~0,
+ .mult = 1<<XEN_SHIFT, /* time directly in nanoseconds */
+ .shift = XEN_SHIFT,
+ .flags = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+/*
+ Xen clockevent implementation
+
+ Xen has two clockevent implementations:
+
+ The old timer_op one works with all released versions of Xen prior
+ to version 3.0.4. This version of the hypervisor provides a
+ single-shot timer with nanosecond resolution. However, sharing the
+ same event channel is a 100Hz tick which is delivered while the
+ vcpu is running. We don't care about or use this tick, but it will
+ cause the core time code to think the timer fired too soon, and
+ will end up resetting it each time. It could be filtered, but
+ doing so has complications when the ktime clocksource is not yet
+ the xen clocksource (ie, at boot time).
+
+ The new vcpu_op-based timer interface allows the tick timer period
+ to be changed or turned off. The tick timer is not useful as a
+ periodic timer because events are only delivered to running vcpus.
+ The one-shot timer can report when a timeout is in the past, so
+ set_next_event is capable of returning -ETIME when appropriate.
+ This interface is used when available.
+*/
+
+
+/*
+ Get a hypervisor absolute time. In theory we could maintain an
+ offset between the kernel's time and the hypervisor's time, and
+ apply that to a kernel's absolute timeout. Unfortunately the
+ hypervisor and kernel times can drift even if the kernel is using
+ the Xen clocksource, because ntp can warp the kernel's clocksource.
+*/
+static s64 get_abs_timeout(unsigned long delta)
+{
+ return xen_clocksource_read() + delta;
+}
+
+static void xen_timerop_set_mode(enum clock_event_mode mode,
+ struct clock_event_device *evt)
+{
+ switch(mode) {
+ case CLOCK_EVT_MODE_PERIODIC:
+ /* unsupported */
+ WARN_ON(1);
+ break;
+
+ case CLOCK_EVT_MODE_ONESHOT:
+ break;
+
+ case CLOCK_EVT_MODE_UNUSED:
+ case CLOCK_EVT_MODE_SHUTDOWN:
+ HYPERVISOR_set_timer_op(0); /* cancel timeout */
+ break;
+ }
+}
+
+static int xen_timerop_set_next_event(unsigned long delta,
+ struct clock_event_device *evt)
+{
+ WARN_ON(evt->mode != CLOCK_EVT_MODE_ONESHOT);
+
+ if (HYPERVISOR_set_timer_op(get_abs_timeout(delta)) < 0)
+ BUG();
+
+ /* We may have missed the deadline, but there's no real way of
+ knowing for sure. If the event was in the past, then we'll
+ get an immediate interrupt. */
+
+ return 0;
+}
+
+static const struct clock_event_device xen_timerop_clockevent = {
+ .name = "xen",
+ .features = CLOCK_EVT_FEAT_ONESHOT,
+
+ .max_delta_ns = 0xffffffff,
+ .min_delta_ns = TIMER_SLOP,
+
+ .mult = 1,
+ .shift = 0,
+ .rating = 500,
+
+ .set_mode = xen_timerop_set_mode,
+ .set_next_event = xen_timerop_set_next_event,
+};
+
+
+
+static void xen_vcpuop_set_mode(enum clock_event_mode mode,
+ struct clock_event_device *evt)
+{
+ int cpu = smp_processor_id();
+
+ switch(mode) {
+ case CLOCK_EVT_MODE_PERIODIC:
+ WARN_ON(1); /* unsupported */
+ break;
+
+ case CLOCK_EVT_MODE_ONESHOT:
+ if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL))
+ BUG();
+ break;
+
+ case CLOCK_EVT_MODE_UNUSED:
+ case CLOCK_EVT_MODE_SHUTDOWN:
+ if (HYPERVISOR_vcpu_op(VCPUOP_stop_singleshot_timer, cpu, NULL) ||
+ HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL))
+ BUG();
+ break;
+ }
+}
+
+static int xen_vcpuop_set_next_event(unsigned long delta,
+ struct clock_event_device *evt)
+{
+ int cpu = smp_processor_id();
+ struct vcpu_set_singleshot_timer single;
+ int ret;
+
+ WARN_ON(evt->mode != CLOCK_EVT_MODE_ONESHOT);
+
+ single.timeout_abs_ns = get_abs_timeout(delta);
+ single.flags = VCPU_SSHOTTMR_future;
+
+ ret = HYPERVISOR_vcpu_op(VCPUOP_set_singleshot_timer, cpu, &single);
+
+ BUG_ON(ret != 0 && ret != -ETIME);
+
+ return ret;
+}
+
+static const struct clock_event_device xen_vcpuop_clockevent = {
+ .name = "xen",
+ .features = CLOCK_EVT_FEAT_ONESHOT,
+
+ .max_delta_ns = 0xffffffff,
+ .min_delta_ns = TIMER_SLOP,
+
+ .mult = 1,
+ .shift = 0,
+ .rating = 500,
+
+ .set_mode = xen_vcpuop_set_mode,
+ .set_next_event = xen_vcpuop_set_next_event,
+};
+
+static const struct clock_event_device *xen_clockevent =
+ &xen_timerop_clockevent;
+static DEFINE_PER_CPU(struct clock_event_device, xen_clock_events);
+
+static irqreturn_t xen_timer_interrupt(int irq, void *dev_id)
+{
+ struct clock_event_device *evt = &__get_cpu_var(xen_clock_events);
+ irqreturn_t ret;
+
+ ret = IRQ_NONE;
+ if (evt->event_handler) {
+ evt->event_handler(evt);
+ ret = IRQ_HANDLED;
+ }
+
+ return ret;
+}
+
+static void xen_setup_timer(int cpu)
+{
+ const char *name;
+ struct clock_event_device *evt;
+ int irq;
+
+ printk("installing Xen timer for CPU %d\n", cpu);
+
+ name = kasprintf(GFP_KERNEL, "timer%d", cpu);
+ if (!name)
+ name = "<timer kasprintf failed>";
+
+ irq = bind_virq_to_irqhandler(VIRQ_TIMER, cpu, xen_timer_interrupt,
+ IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
+ name, NULL);
+
+ evt = &get_cpu_var(xen_clock_events);
+ memcpy(evt, xen_clockevent, sizeof(*evt));
+
+ evt->cpumask = cpumask_of_cpu(cpu);
+ evt->irq = irq;
+ clockevents_register_device(evt);
+
+ put_cpu_var(xen_clock_events);
+}
+
+__init void xen_time_init(void)
+{
+ int cpu = smp_processor_id();
+
+ get_time_values_from_xen();
+
+ clocksource_register(&xen_clocksource);
+
+ if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL) == 0) {
+ /* Successfully turned off 100hz tick, so we have the
+ vcpuop-based timer interface */
+ printk(KERN_DEBUG "Xen: using vcpuop timer interface\n");
+ xen_clockevent = &xen_vcpuop_clockevent;
+ }
+
+ /* Set initial system time with full resolution */
+ xen_read_wallclock(&xtime);
+ set_normalized_timespec(&wall_to_monotonic,
+ -xtime.tv_sec, -xtime.tv_nsec);
+
+ tsc_disable = 0;
+
+ xen_setup_timer(cpu);
+}

--