Re: [Xen-devel] repeatable time jump

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> 
> " linux-2.6.8.1-xen-sparse/arch/xen/i386/kernel/time.c and see what
> " comes out when you run your test. It's also interesting to see
> " what output comes out after the time skip whenever you run date. 
> 
> OK, I pulled and patched.   I ran date in a loop as xenU was shutdown
> and time jumped 4293 secs from 1096637912.846396000 to 1096642205.961018000
> ntpd was running in xen0.

David, Peri:

I suspect you guys are seeing manifestations of the same
bug. It's odd that you only see it on some machines, but it might
be due to the relative error between the RTC and CPU clocks or
such like.

Please can you try the new patch which may give a little more
information.

Thanks,
Ian


--- 
/usr/groups/xeno/BK/xeno.bk/linux-2.6.8.1-xen-sparse/arch/xen/i386/kernel/time.c
    2004-10-01 16:01:03.000000000 +0100
+++ arch/xen/i386/kernel/time.c 2004-10-01 16:10:06.000000000 +0100
@@ -114,28 +114,34 @@
 
 #define NS_PER_TICK (1000000000ULL/HZ)
 
-#define HANDLE_USEC_UNDERFLOW(_tv) do {                \
+#define HANDLE_USEC_UNDERFLOW(_tv) do {        int i=0;        \
        while ((_tv).tv_usec < 0) {             \
                (_tv).tv_usec += USEC_PER_SEC;  \
                (_tv).tv_sec--;                 \
-       }                                       \
+       }if(i>100)printk(KERN_ALERT"USEC_UNDER %d\n",i);        \
 } while (0)
-#define HANDLE_USEC_OVERFLOW(_tv) do {         \
+#define HANDLE_USEC_OVERFLOW(_tv) do { int i=0;        \
        while ((_tv).tv_usec >= USEC_PER_SEC) { \
                (_tv).tv_usec -= USEC_PER_SEC;  \
-               (_tv).tv_sec++;                 \
-       }                                       \
+               (_tv).tv_sec++; i++;            \
+       }if(i>100)printk(KERN_ALERT"USEC_OVER %d\n",i); \
 } while (0)
 static inline void __normalize_time(time_t *sec, s64 *nsec)
 {
+int i=0,j=0;
        while (*nsec >= NSEC_PER_SEC) {
                (*nsec) -= NSEC_PER_SEC;
                (*sec)++;
+               i++;
        }
        while (*nsec < 0) {
                (*nsec) += NSEC_PER_SEC;
                (*sec)--;
+               j++;
        }
+
+if( i>100 || j>100 ) printk(KERN_ALERT"normalize time %d %d\n",i,j);
+
 }
 
 /* Does this guest OS track Xen time, or set its wall clock independently? */
@@ -155,6 +161,8 @@
  */
 static void __get_time_values_from_xen(void)
 {
+long last = shadow_tv.tv_sec;
+
        shared_info_t *s = HYPERVISOR_shared_info;
 
        do {
@@ -169,6 +177,7 @@
        while (shadow_time_version != s->time_version1);
 
        cur_timer->mark_offset();
+if( shadow_tv.tv_sec-last > 600 ) printk(KERN_ALERT"**** 
__get_time_values_from_xen(void) JUPMED!\n");
 }
 
 #define TIME_VALUES_UP_TO_DATE \
@@ -227,18 +236,26 @@
                        write_seqlock_irqsave(&xtime_lock, flags);
                        __get_time_values_from_xen();
                        write_sequnlock_irqrestore(&xtime_lock, flags);
+printk(KERN_ALERT"GTOD Try again %ld %lld\n", shadow_tv.tv_sec,
+       shadow_system_time);
                        continue;
                }
        } while (read_seqretry(&xtime_lock, seq));
 
+{
+int z=0;
        while (usec >= USEC_PER_SEC) {
                usec -= USEC_PER_SEC;
                sec++;
+               z++;
        }
+if(z>100) printk(KERN_ALERT"GTOD JUMP %d\n",z);
+}
 
        /* Ensure that time-of-day is monotonically increasing. */
        if ((sec < last_seen_tv.tv_sec) ||
            ((sec == last_seen_tv.tv_sec) && (usec < last_seen_tv.tv_usec))) {
+printk(KERN_ALERT"Clamp time %ld %ld\n",sec,last_seen_tv.tv_sec); 
                sec = last_seen_tv.tv_sec;
                usec = last_seen_tv.tv_usec;
        } else {
@@ -364,6 +381,7 @@
                                        struct pt_regs *regs)
 {
        s64 delta;
+       unsigned int ticks = 0;
        long sec_diff;
 
        __get_time_values_from_xen();
@@ -378,9 +396,14 @@
 
        /* Process elapsed jiffies since last call. */
        while (delta >= NS_PER_TICK) {
+               ticks++;
                delta -= NS_PER_TICK;
                processed_system_time += NS_PER_TICK;
-               do_timer_interrupt_hook(regs);
+       }
+
+       if (ticks != 0) {
+               jiffies_64 += ticks - 1;
+               do_timer_interrupt_hook(regs); /* implicit 'jiffies_64++' */
        }
 
        /*


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