RE: [PATCH] [RFC] Building guests on monotonic Xen system time

["Dan Magenheimer" <dan.magenheimer@oracle.com>]

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As I look at this more, I'm convincing myself that
it may not make sense to build the guest TSC on top
of Xen system time and only the guest virtual platform
timer(s) should be built on Xen system time (and should
be monotonically non-decreasing).

Why? Scaling and adjusting of xen-time-based-tsc will
be very difficult to coordinate with processor-based-tsc.
We need to always ensure that A < B < C for a guest
executing:

rdtsc(A) /* untrapped */
emulated_rdtsc(B)
rdtsc(C) /* untrapped */

Further, OS's use TSC as a highest-resolution time source
with knowledge that TSCs on different processors may
not be synchronized, whereas they assume that a platform
timer is one-per-system and monotonically increasing.

Keir, if you disagree and see guest-TSC-on-Xen-system-time
as an absolute must, please let me know.

Unfortunately, hvm_get/set_system_time() are #defined to
be hvm_get/set_system_tsc() so the usage is pretty muddled.
I think the attached patch has teased the two apart though.

Note this is still RFC, not a finished patch.

> -----Original Message-----
> From: xen-devel-bounces@lists.xensource.com
> [mailto:xen-devel-bounces@lists.xensource.com]On Behalf Of Dan
> Magenheimer
> Sent: Friday, May 16, 2008 11:31 AM
> To: Xen-Devel (E-mail)
> Subject: [Xen-devel] [PATCH] [RFC] Building guests on monotonic Xen
> system time
> 
> 
> Currently, hvm guest platform timers are built on top of the tsc.
> Even though the guest believes it is utilizing a monotonic timesource
> (such as pit, hpet, or pmtimer), all of these plumb down to an
> rdtsc instruction.
> 
> Since on many SMP platforms tsc's in different processors are not
> synchronized, VMs re-scheduled from a "fast tsc" processor to
> a "slow tsc" processor may experience "time going backwards".
> This is discussed in the following thread:
> 
> http://lists.xensource.com/archives/html/xen-devel/2008-04/msg
00277.html

The fix proposed by Keir is that "The logic in vpt.c should
be fixed to use Xen's concept of system time and everything,
guest TSC included, should be derived from that."

The attached patch is a first attempt to derive all
guest timers from Xen's system time... and also to ensure
that system time is non-decreasing. I don't believe the
patch is complete... and possibly not even correct.
For example, I'm concerned that Xen's system time uses
different units than a guest tsc and I don't recall if
all guest tsc accesses are trapped.

Dan

===================================
Thanks... for the memory
I really could use more / My throughput's on the floor
The balloon is flat / My swap disk's fat / I've OOM's in store
Overcommitted so much
(with apologies to the late great Bob Hope)

[-- Attachment #2: hvmstime2.patch --]
[-- Type: application/octet-stream, Size: 17363 bytes --]

diff -r e3b13e1ecf6c xen/arch/x86/hvm/hpet.c
--- a/xen/arch/x86/hvm/hpet.c	Thu May 15 15:10:05 2008 +0100
+++ b/xen/arch/x86/hvm/hpet.c	Mon May 19 12:14:22 2008 -0600
@@ -29,9 +29,9 @@
 #define S_TO_NS  1000000000ULL           /* 1s  = 10^9  ns */
 #define S_TO_FS  1000000000000000ULL     /* 1s  = 10^15 fs */
 
-/* Frequency_of_TSC / frequency_of_HPET = 32 */
-#define TSC_PER_HPET_TICK 32
-#define guest_time_hpet(v) (hvm_get_guest_time(v) / TSC_PER_HPET_TICK)
+/* Frequency_of_Xen_systeme_time / frequency_of_HPET = 16 */
+#define STIME_PER_HPET_TICK 16
+#define guest_time_hpet(v) (hvm_get_guest_time_mono(v) / STIME_PER_HPET_TICK)
 
 #define HPET_ID         0x000
 #define HPET_PERIOD     0x004
@@ -192,7 +192,7 @@ static void hpet_stop_timer(HPETState *h
 
 /* the number of HPET tick that stands for
  * 1/(2^10) second, namely, 0.9765625 milliseconds */
-#define  HPET_TINY_TIME_SPAN  ((h->tsc_freq >> 10) / TSC_PER_HPET_TICK)
+#define  HPET_TINY_TIME_SPAN  ((h->stime_freq >> 10) / STIME_PER_HPET_TICK)
 
 static void hpet_set_timer(HPETState *h, unsigned int tn)
 {
@@ -558,17 +558,17 @@ void hpet_init(struct vcpu *v)
     spin_lock_init(&h->lock);
 
     h->vcpu = v;
-    h->tsc_freq = ticks_per_sec(v);
+    h->stime_freq = S_TO_NS;
 
-    h->hpet_to_ns_scale = ((S_TO_NS * TSC_PER_HPET_TICK) << 10) / h->tsc_freq;
+    h->hpet_to_ns_scale = ((S_TO_NS * STIME_PER_HPET_TICK) << 10) / h->stime_freq;
     h->hpet_to_ns_limit = ~0ULL / h->hpet_to_ns_scale;
 
     /* 64-bit main counter; 3 timers supported; LegacyReplacementRoute. */
     h->hpet.capability = 0x8086A201ULL;
 
     /* This is the number of femptoseconds per HPET tick. */
-    /* Here we define HPET's frequency to be 1/32 of the TSC's */
-    h->hpet.capability |= ((S_TO_FS*TSC_PER_HPET_TICK/h->tsc_freq) << 32);
+    /* Here we define HPET's frequency to be 1/16 of Xen system time */
+    h->hpet.capability |= ((S_TO_FS*STIME_PER_HPET_TICK/h->stime_freq) << 32);
 
     for ( i = 0; i < HPET_TIMER_NUM; i++ )
     {
diff -r e3b13e1ecf6c xen/arch/x86/hvm/hvm.c
--- a/xen/arch/x86/hvm/hvm.c	Thu May 15 15:10:05 2008 +0100
+++ b/xen/arch/x86/hvm/hvm.c	Mon May 19 12:14:22 2008 -0600
@@ -31,6 +31,7 @@
 #include <xen/hypercall.h>
 #include <xen/guest_access.h>
 #include <xen/event.h>
+#include <xen/time.h>
 #include <asm/current.h>
 #include <asm/e820.h>
 #include <asm/io.h>
@@ -139,7 +140,6 @@ void hvm_set_guest_tsc(struct vcpu *v, u
     u64 host_tsc;
 
     rdtscll(host_tsc);
-
     v->arch.hvm_vcpu.cache_tsc_offset = guest_tsc - host_tsc;
     hvm_funcs.set_tsc_offset(v, v->arch.hvm_vcpu.cache_tsc_offset);
 }
@@ -150,6 +150,28 @@ u64 hvm_get_guest_tsc(struct vcpu *v)
 
     rdtscll(host_tsc);
     return host_tsc + v->arch.hvm_vcpu.cache_tsc_offset;
+}
+
+void hvm_set_guest_time(struct vcpu *v, u64 guest_time)
+{
+    u64 host_time = (u64)get_s_time_mono();
+
+    v->arch.hvm_vcpu.cache_time_offset = guest_time - host_time;
+}
+
+u64 hvm_get_guest_time(struct vcpu *v)
+{
+    u64 host_time = (u64)get_s_time();
+
+    return host_time + v->arch.hvm_vcpu.cache_time_offset;
+}
+
+
+u64 hvm_get_guest_time_mono(struct vcpu *v)
+{
+    u64 host_time = (u64)get_s_time_mono();
+
+    return host_time + v->arch.hvm_vcpu.cache_time_offset;
 }
 
 void hvm_migrate_timers(struct vcpu *v)
@@ -1632,7 +1654,7 @@ int hvm_msr_read_intercept(struct cpu_us
     switch ( ecx )
     {
     case MSR_IA32_TSC:
-        msr_content = hvm_get_guest_time(v);
+        msr_content = hvm_get_guest_tsc(v);
         break;
 
     case MSR_IA32_APICBASE:
@@ -1725,7 +1747,7 @@ int hvm_msr_write_intercept(struct cpu_u
     switch ( ecx )
     {
      case MSR_IA32_TSC:
-        hvm_set_guest_time(v, msr_content);
+        hvm_set_guest_tsc(v, msr_content);
         pt_reset(v);
         break;
 
diff -r e3b13e1ecf6c xen/arch/x86/hvm/i8254.c
--- a/xen/arch/x86/hvm/i8254.c	Thu May 15 15:10:05 2008 +0100
+++ b/xen/arch/x86/hvm/i8254.c	Mon May 19 12:14:22 2008 -0600
@@ -86,7 +86,7 @@ static int pit_get_count(PITState *pit, 
 
     ASSERT(spin_is_locked(&pit->lock));
 
-    d = muldiv64(hvm_get_guest_time(v) - pit->count_load_time[channel],
+    d = muldiv64(hvm_get_guest_time_mono(v) - pit->count_load_time[channel],
                  PIT_FREQ, ticks_per_sec(v));
 
     switch ( c->mode )
@@ -117,7 +117,7 @@ static int pit_get_out(PITState *pit, in
 
     ASSERT(spin_is_locked(&pit->lock));
 
-    d = muldiv64(hvm_get_guest_time(v) - pit->count_load_time[channel], 
+    d = muldiv64(hvm_get_guest_time_mono(v) - pit->count_load_time[channel], 
                  PIT_FREQ, ticks_per_sec(v));
 
     switch ( s->mode )
@@ -164,7 +164,7 @@ static void pit_set_gate(PITState *pit, 
     case 3:
         /* Restart counting on rising edge. */
         if ( s->gate < val )
-            pit->count_load_time[channel] = hvm_get_guest_time(v);
+            pit->count_load_time[channel] = hvm_get_guest_time_mono(v);
         break;
     }
 
@@ -180,7 +180,7 @@ static void pit_time_fired(struct vcpu *
 static void pit_time_fired(struct vcpu *v, void *priv)
 {
     uint64_t *count_load_time = priv;
-    *count_load_time = hvm_get_guest_time(v);
+    *count_load_time = hvm_get_guest_time_mono(v);
 }
 
 static void pit_load_count(PITState *pit, int channel, int val)
@@ -195,9 +195,13 @@ static void pit_load_count(PITState *pit
         val = 0x10000;
 
     if ( v == NULL )
+        gdprintk(XENLOG_ERR, "NULL vcpu in pit_load_count.\n");
+    /*
         rdtscll(pit->count_load_time[channel]);
     else
-        pit->count_load_time[channel] = hvm_get_guest_time(v);
+*/
+/*    ASSERT(v); */
+        pit->count_load_time[channel] = hvm_get_guest_time_mono(v);
     s->count = val;
     period = DIV_ROUND((val * 1000000000ULL), PIT_FREQ);
 
@@ -435,7 +439,7 @@ static int pit_load(struct domain *d, hv
      * time jitter here, but the wall-clock will have jumped massively, so 
      * we hope the guest can handle it.
      */
-    pit->pt0.last_plt_gtime = hvm_get_guest_time(d->vcpu[0]);
+    pit->pt0.last_plt_gtime = hvm_get_guest_time_mono(d->vcpu[0]);
     for ( i = 0; i < 3; i++ )
         pit_load_count(pit, i, pit->hw.channels[i].count);
 
diff -r e3b13e1ecf6c xen/arch/x86/hvm/pmtimer.c
--- a/xen/arch/x86/hvm/pmtimer.c	Thu May 15 15:10:05 2008 +0100
+++ b/xen/arch/x86/hvm/pmtimer.c	Mon May 19 12:14:22 2008 -0600
@@ -71,7 +71,7 @@ static void pmt_update_time(PMTState *s)
     ASSERT(spin_is_locked(&s->lock));
 
     /* Update the timer */
-    curr_gtime = hvm_get_guest_time(s->vcpu);
+    curr_gtime = hvm_get_guest_time_mono(s->vcpu);
     s->pm.tmr_val += ((curr_gtime - s->last_gtime) * s->scale) >> 32;
     s->pm.tmr_val &= TMR_VAL_MASK;
     s->last_gtime = curr_gtime;
@@ -238,7 +238,7 @@ static int pmtimer_load(struct domain *d
     }
 
     /* Calculate future counter values from now. */
-    s->last_gtime = hvm_get_guest_time(s->vcpu);
+    s->last_gtime = hvm_get_guest_time_mono(s->vcpu);
 
     /* Set the SCI state from the registers */ 
     pmt_update_sci(s);
diff -r e3b13e1ecf6c xen/arch/x86/hvm/svm/svm.c
--- a/xen/arch/x86/hvm/svm/svm.c	Thu May 15 15:10:05 2008 +0100
+++ b/xen/arch/x86/hvm/svm/svm.c	Mon May 19 12:14:22 2008 -0600
@@ -299,7 +299,7 @@ static void svm_save_cpu_state(struct vc
     data->msr_efer         = v->arch.hvm_vcpu.guest_efer;
     data->msr_flags        = -1ULL;
 
-    data->tsc = hvm_get_guest_time(v);
+    data->tsc = hvm_get_guest_tsc(v);
 }
 
 
@@ -315,7 +315,7 @@ static void svm_load_cpu_state(struct vc
     v->arch.hvm_vcpu.guest_efer = data->msr_efer;
     svm_update_guest_efer(v);
 
-    hvm_set_guest_time(v, data->tsc);
+    hvm_set_guest_tsc(v, data->tsc);
 }
 
 static void svm_save_vmcb_ctxt(struct vcpu *v, struct hvm_hw_cpu *ctxt)
@@ -583,6 +583,12 @@ static void svm_set_tsc_offset(struct vc
     v->arch.hvm_svm.vmcb->tsc_offset = offset;
 }
 
+
+static void svm_set_time_offset(struct vcpu *v, u64 offset)
+{
+    v->arch.hvm_vcpu.cache_time_offset = offset;
+}
+
 static void svm_init_hypercall_page(struct domain *d, void *hypercall_page)
 {
     char *p;
@@ -790,6 +796,7 @@ static struct hvm_function_table svm_fun
     .update_guest_efer    = svm_update_guest_efer,
     .flush_guest_tlbs     = svm_flush_guest_tlbs,
     .set_tsc_offset       = svm_set_tsc_offset,
+    .set_time_offset      = svm_set_time_offset,
     .inject_exception     = svm_inject_exception,
     .init_hypercall_page  = svm_init_hypercall_page,
     .event_pending        = svm_event_pending,
diff -r e3b13e1ecf6c xen/arch/x86/hvm/vlapic.c
--- a/xen/arch/x86/hvm/vlapic.c	Thu May 15 15:10:05 2008 +0100
+++ b/xen/arch/x86/hvm/vlapic.c	Mon May 19 12:14:22 2008 -0600
@@ -535,8 +535,8 @@ static uint32_t vlapic_get_tmcct(struct 
     uint32_t tmcct, tmict = vlapic_get_reg(vlapic, APIC_TMICT);
     uint64_t counter_passed;
 
-    counter_passed = ((hvm_get_guest_time(v) - vlapic->timer_last_update)
-                      * 1000000000ULL / ticks_per_sec(v)
+    counter_passed = ((hvm_get_guest_time_mono(v) - vlapic->timer_last_update)
+                      /* * 1000000000ULL / ticks_per_sec(v) */
                       / APIC_BUS_CYCLE_NS / vlapic->hw.timer_divisor);
     tmcct = tmict - counter_passed;
 
@@ -638,7 +638,7 @@ static int vlapic_read(
 
 void vlapic_pt_cb(struct vcpu *v, void *data)
 {
-    *(s_time_t *)data = hvm_get_guest_time(v);
+    *(s_time_t *)data = hvm_get_guest_time_mono(v);
 }
 
 static int vlapic_write(struct vcpu *v, unsigned long address,
diff -r e3b13e1ecf6c xen/arch/x86/hvm/vmx/vmx.c
--- a/xen/arch/x86/hvm/vmx/vmx.c	Thu May 15 15:10:05 2008 +0100
+++ b/xen/arch/x86/hvm/vmx/vmx.c	Mon May 19 12:14:22 2008 -0600
@@ -607,7 +607,7 @@ static void vmx_save_cpu_state(struct vc
     data->msr_syscall_mask = guest_state->msrs[VMX_INDEX_MSR_SYSCALL_MASK];
 #endif
 
-    data->tsc = hvm_get_guest_time(v);
+    data->tsc = hvm_get_guest_tsc(v);
 }
 
 static void vmx_load_cpu_state(struct vcpu *v, struct hvm_hw_cpu *data)
@@ -625,7 +625,7 @@ static void vmx_load_cpu_state(struct vc
     v->arch.hvm_vmx.shadow_gs = data->shadow_gs;
 #endif
 
-    hvm_set_guest_time(v, data->tsc);
+    hvm_set_guest_tsc(v, data->tsc);
 }
 
 
@@ -866,6 +866,11 @@ static void vmx_set_tsc_offset(struct vc
     __vmwrite(TSC_OFFSET_HIGH, offset >> 32);
 #endif
     vmx_vmcs_exit(v);
+}
+
+static void vmx_set_time_offset(struct vcpu *v, u64 offset)
+{
+    v->arch.hvm_vcpu.cache_time_offset = offset;
 }
 
 void do_nmi(struct cpu_user_regs *);
@@ -1186,6 +1191,7 @@ static struct hvm_function_table vmx_fun
     .update_guest_efer    = vmx_update_guest_efer,
     .flush_guest_tlbs     = vmx_flush_guest_tlbs,
     .set_tsc_offset       = vmx_set_tsc_offset,
+    .set_time_offset       = vmx_set_time_offset,
     .inject_exception     = vmx_inject_exception,
     .init_hypercall_page  = vmx_init_hypercall_page,
     .event_pending        = vmx_event_pending,
diff -r e3b13e1ecf6c xen/arch/x86/hvm/vpt.c
--- a/xen/arch/x86/hvm/vpt.c	Thu May 15 15:10:05 2008 +0100
+++ b/xen/arch/x86/hvm/vpt.c	Mon May 19 12:14:22 2008 -0600
@@ -108,7 +108,7 @@ static void pt_freeze_time(struct vcpu *
     if ( !mode_is(v->domain, delay_for_missed_ticks) )
         return;
 
-    v->arch.hvm_vcpu.guest_time = hvm_get_guest_time(v);
+    v->arch.hvm_vcpu.guest_time = hvm_get_guest_time_mono(v);
 }
 
 static void pt_thaw_time(struct vcpu *v)
@@ -267,7 +267,7 @@ void pt_intr_post(struct vcpu *v, struct
         if ( mode_is(v->domain, one_missed_tick_pending) ||
              mode_is(v->domain, no_missed_ticks_pending) )
         {
-            pt->last_plt_gtime = hvm_get_guest_time(v);
+            pt->last_plt_gtime = hvm_get_guest_time_mono(v);
             pt->pending_intr_nr = 0; /* 'collapse' all missed ticks */
         }
         else
@@ -278,7 +278,7 @@ void pt_intr_post(struct vcpu *v, struct
     }
 
     if ( mode_is(v->domain, delay_for_missed_ticks) &&
-         (hvm_get_guest_time(v) < pt->last_plt_gtime) )
+         (hvm_get_guest_time_mono(v) < pt->last_plt_gtime) )
         hvm_set_guest_time(v, pt->last_plt_gtime);
 
     cb = pt->cb;
@@ -300,7 +300,7 @@ void pt_reset(struct vcpu *v)
     list_for_each_entry ( pt, head, list )
     {
         pt->pending_intr_nr = 0;
-        pt->last_plt_gtime = hvm_get_guest_time(pt->vcpu);
+        pt->last_plt_gtime = hvm_get_guest_time_mono(pt->vcpu);
         pt->scheduled = NOW() + pt->period;
         set_timer(&pt->timer, pt->scheduled);
     }
@@ -346,9 +346,9 @@ void create_periodic_time(
 
     pt->period = period;
     pt->vcpu = v;
-    pt->last_plt_gtime = hvm_get_guest_time(pt->vcpu);
+    pt->last_plt_gtime = hvm_get_guest_time_mono(pt->vcpu);
     pt->irq = irq;
-    pt->period_cycles = (u64)period * cpu_khz / 1000000L;
+    pt->period_cycles = (u64)period /* * cpu_khz / 1000000L*/;
     pt->one_shot = one_shot;
     pt->scheduled = NOW() + period;
     /*
diff -r e3b13e1ecf6c xen/arch/x86/time.c
--- a/xen/arch/x86/time.c	Thu May 15 15:10:05 2008 +0100
+++ b/xen/arch/x86/time.c	Mon May 19 12:14:22 2008 -0600
@@ -535,6 +535,8 @@ static s_time_t read_platform_stime(void
     return stime;
 }
 
+extern void get_s_time_mono_init(void);
+
 static void platform_time_calibration(void)
 {
     u64 count;
@@ -593,6 +595,7 @@ static void init_platform_timer(void)
     plt_overflow(NULL);
 
     platform_timer_stamp = plt_stamp64;
+    get_s_time_mono_init();
 
     printk("Platform timer is %s %s\n",
            freq_string(pts->frequency), pts->name);
@@ -728,6 +731,29 @@ s_time_t get_s_time(void)
     rdtscll(tsc);
     delta = tsc - t->local_tsc_stamp;
     now = t->stime_local_stamp + scale_delta(delta, &t->tsc_scale);
+
+    return now;
+}
+
+spinlock_t get_s_time_mono_lock;
+
+void get_s_time_mono_init(void)
+{
+    spin_lock_init(&get_s_time_mono_lock);
+}
+
+s_time_t get_s_time_mono(void)
+{
+    s_time_t now;
+    static s_time_t last = (s_time_t)0;
+
+    spin_lock(&get_s_time_mono_lock);
+    now = get_s_time();
+    if (now > last)
+        last = now;
+    else
+        now = last;
+    spin_unlock(&get_s_time_mono_lock);
 
     return now;
 }
diff -r e3b13e1ecf6c xen/include/asm-x86/hvm/hvm.h
--- a/xen/include/asm-x86/hvm/hvm.h	Thu May 15 15:10:05 2008 +0100
+++ b/xen/include/asm-x86/hvm/hvm.h	Mon May 19 12:14:22 2008 -0600
@@ -107,6 +107,8 @@ struct hvm_function_table {
 
     void (*set_tsc_offset)(struct vcpu *v, u64 offset);
 
+    void (*set_time_offset)(struct vcpu *v, u64 offset);
+
     void (*inject_exception)(unsigned int trapnr, int errcode,
                              unsigned long cr2);
 
@@ -146,8 +148,13 @@ void hvm_send_assist_req(struct vcpu *v)
 
 void hvm_set_guest_tsc(struct vcpu *v, u64 guest_tsc);
 u64 hvm_get_guest_tsc(struct vcpu *v);
+void hvm_set_guest_time(struct vcpu *v, u64 guest_time);
+u64 hvm_get_guest_time(struct vcpu *v);
+u64 hvm_get_guest_time_mono(struct vcpu *v);
+/*
 #define hvm_set_guest_time(vcpu, gtime) hvm_set_guest_tsc(vcpu, gtime)
 #define hvm_get_guest_time(vcpu)        hvm_get_guest_tsc(vcpu)
+*/
 
 #define hvm_paging_enabled(v) \
     (!!((v)->arch.hvm_vcpu.guest_cr[0] & X86_CR0_PG))
diff -r e3b13e1ecf6c xen/include/asm-x86/hvm/vcpu.h
--- a/xen/include/asm-x86/hvm/vcpu.h	Thu May 15 15:10:05 2008 +0100
+++ b/xen/include/asm-x86/hvm/vcpu.h	Mon May 19 12:14:22 2008 -0600
@@ -50,6 +50,7 @@ struct hvm_vcpu {
     struct vlapic       vlapic;
     s64                 cache_tsc_offset;
     u64                 guest_time;
+    s64                 cache_time_offset;
 
     /* Lock and list for virtual platform timers. */
     spinlock_t          tm_lock;
diff -r e3b13e1ecf6c xen/include/asm-x86/hvm/vmx/vmx.h
--- a/xen/include/asm-x86/hvm/vmx/vmx.h	Thu May 15 15:10:05 2008 +0100
+++ b/xen/include/asm-x86/hvm/vmx/vmx.h	Mon May 19 12:14:22 2008 -0600
@@ -49,7 +49,6 @@ void vmx_asm_do_vmentry(void);
 void vmx_asm_do_vmentry(void);
 void vmx_intr_assist(void);
 void vmx_do_resume(struct vcpu *);
-void set_guest_time(struct vcpu *v, u64 gtime);
 void vmx_vlapic_msr_changed(struct vcpu *v);
 void vmx_realmode(struct cpu_user_regs *regs);
 
diff -r e3b13e1ecf6c xen/include/asm-x86/hvm/vpt.h
--- a/xen/include/asm-x86/hvm/vpt.h	Thu May 15 15:10:05 2008 +0100
+++ b/xen/include/asm-x86/hvm/vpt.h	Mon May 19 12:14:22 2008 -0600
@@ -57,7 +57,7 @@ typedef struct HPETState {
 typedef struct HPETState {
     struct hpet_registers hpet;
     struct vcpu *vcpu;
-    uint64_t tsc_freq;
+    uint64_t stime_freq;
     uint64_t hpet_to_ns_scale; /* hpet ticks to ns (multiplied by 2^10) */
     uint64_t hpet_to_ns_limit; /* max hpet ticks convertable to ns      */
     uint64_t mc_offset;
diff -r e3b13e1ecf6c xen/include/xen/time.h
--- a/xen/include/xen/time.h	Thu May 15 15:10:05 2008 +0100
+++ b/xen/include/xen/time.h	Mon May 19 12:14:22 2008 -0600
@@ -24,6 +24,8 @@ struct domain;
  * System Time
  * 64 bit value containing the nanoseconds elapsed since boot time.
  * This value is adjusted by frequency drift.
+ * mono version guarantees that consecutive reads are non-decreasing,
+ * (e.g. when first read is on a different processor than second read)
  * NOW() returns the current time.
  * The other macros are for convenience to approximate short intervals
  * of real time into system time 
@@ -32,6 +34,7 @@ typedef s64 s_time_t;
 typedef s64 s_time_t;
 
 s_time_t get_s_time(void);
+s_time_t get_s_time_mono(void);
 unsigned long get_localtime(struct domain *d);
 
 struct tm {

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