Re: [Xen-devel] [PATCH 0/2] Improve hpet accuracy

[Dave Winchell <dwinchell@xxxxxxxxxxxxxxx>]

Keir, Dan:

Although I plan to break up the patch, etc., I'm posting
this fix to the patch for anyone who might be interested.

thanks,
Dave

# This is a BitKeeper generated diff -Nru style patch.
#
# ChangeSet
#   2008/06/10 12:20:48-04:00 winchell@xxxxxxxxxxxxxxxxxxxxxxxxxx 
#   vi-patch: xen-hpet
#   
#   Bug Id: 6057 
#   
#   Reviewed by: Robert
#   
#   SUMMARY: Fix wrap issue in monotonic s_time().
# 
# xen/arch/x86/time.c
#   2008/06/10 12:20:48-04:00 winchell@xxxxxxxxxxxxxxxxxxxxxxxxxx +3 -2
#   Fix wrap issue in monotonic s_time().
# 
diff -Nru a/xen/arch/x86/time.c b/xen/arch/x86/time.c
--- a/xen/arch/x86/time.c       2008-06-10 13:08:39 -04:00
+++ b/xen/arch/x86/time.c       2008-06-10 13:08:39 -04:00
@@ -534,7 +534,7 @@
     u64 count;
     unsigned long flags;
     struct cpu_time *t = &this_cpu(cpu_time);
-    u64 tsc, delta;
+    u64 tsc, delta, diff;
     s_time_t now;
 
     if(hpet_main_counter_phys_avoid_hdw || !hpet_physical_inited) {
@@ -542,7 +542,8 @@
         rdtscll(tsc);
         delta = tsc - t->local_tsc_stamp;
         now = t->stime_local_stamp + scale_delta(delta, &t->tsc_scale);
-        if(now > get_s_time_mon.last_ret)
+        diff = (u64)now - (u64)get_s_time_mon.last_ret;
+        if((s64)diff > (s64)0)
             get_s_time_mon.last_ret = now;
         else
             now = get_s_time_mon.last_ret;

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