File 576001df-x86-time-use-local-stamp-in-TSC-calibration-fast-path.patch of Package xen.3880

References: bsc#970135

# Commit b64438c7c1495a7580d1bb9d8ba644f3705e1ffb
# Date 2016-06-14 15:08:47 +0200
# Author Jan Beulich <jbeulich@suse.com>
# Committer Jan Beulich <jbeulich@suse.com>
x86/time: use correct (local) time stamp in constant-TSC calibration fast path

This looks like a copy and paste mistake in commit 1b6a99892d ("x86:
Simpler time handling when TSC is constant across all power saving
states"), responsible for occasional many-microsecond cross-CPU skew of
what NOW() returns.

Also improve the correlation between local TSC and stime stamps
obtained at the end of the two calibration handlers: Compute the stime
one from the TSC one, instead of doing another rdtsc() for that
compuation.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -751,19 +751,25 @@ static unsigned long get_cmos_time(void)
  * System Time
  ***************************************************************************/
 
-s_time_t get_s_time(void)
+static s_time_t get_s_time_fixed(u64 tsc)
 {
     struct cpu_time *t = &this_cpu(cpu_time);
-    u64 tsc, delta;
+    u64 delta;
     s_time_t now;
 
-    rdtscll(tsc);
+    if ( !tsc )
+        rdtscll(tsc);
     delta = tsc - t->local_tsc_stamp;
     now = t->stime_local_stamp + scale_delta(delta, &t->tsc_scale);
 
     return now;
 }
 
+s_time_t get_s_time(void)
+{
+    return get_s_time_fixed(0);
+}
+
 uint64_t tsc_ticks2ns(uint64_t ticks)
 {
     struct cpu_time *t = &this_cpu(cpu_time);
@@ -1025,7 +1031,7 @@ static void local_time_calibration(void)
         /* Atomically read cpu_calibration struct and write cpu_time struct. */
         local_irq_disable();
         t->local_tsc_stamp    = c->local_tsc_stamp;
-        t->stime_local_stamp  = c->stime_master_stamp;
+        t->stime_local_stamp  = c->stime_local_stamp;
         t->stime_master_stamp = c->stime_master_stamp;
         local_irq_enable();
         update_vcpu_system_time(current);
@@ -1302,7 +1308,7 @@ static void time_calibration_tsc_rendezv
     }
 
     rdtscll(c->local_tsc_stamp);
-    c->stime_local_stamp = get_s_time();
+    c->stime_local_stamp = get_s_time_fixed(c->local_tsc_stamp);
     c->stime_master_stamp = r->master_stime;
 
     raise_softirq(TIME_CALIBRATE_SOFTIRQ);
@@ -1332,7 +1338,7 @@ static void time_calibration_std_rendezv
     }
 
     rdtscll(c->local_tsc_stamp);
-    c->stime_local_stamp = get_s_time();
+    c->stime_local_stamp = get_s_time_fixed(c->local_tsc_stamp);
     c->stime_master_stamp = r->master_stime;
 
     raise_softirq(TIME_CALIBRATE_SOFTIRQ);