[PATCH RFC 4/6] x86/time: refactor read_platform_stime()

[Joao Martins <joao.m.martins@oracle.com>]

To fetch the last read from the clocksource which was used to
calculate system_time. In the case of clocksource=tsc we will
use it to set tsc_timestamp.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
 xen/arch/x86/time.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index df42d31..3f96ce6 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -509,6 +509,7 @@ static s_time_t stime_platform_stamp; /* System time at below platform time */
 static u64 platform_timer_stamp;      /* Platform time at above system time */
 static u64 plt_stamp64;          /* 64-bit platform counter stamp           */
 static u64 plt_stamp;            /* hardware-width platform counter stamp   */
+static u64 plt_stamp_counter;    /* last read since read_counter */
 static struct timer plt_overflow_timer;
 
 static s_time_t __read_platform_stime(u64 platform_time)
@@ -567,7 +568,7 @@ static void plt_overflow(void *unused)
     set_timer(&plt_overflow_timer, NOW() + plt_overflow_period);
 }
 
-static s_time_t read_platform_stime(void)
+static s_time_t read_platform_stime(u64 *stamp)
 {
     u64 count;
     s_time_t stime;
@@ -575,8 +576,11 @@ static s_time_t read_platform_stime(void)
     ASSERT(!local_irq_is_enabled());
 
     spin_lock(&platform_timer_lock);
-    count = plt_stamp64 + ((plt_src.read_counter() - plt_stamp) & plt_mask);
+    plt_stamp_counter = plt_src.read_counter();
+    count = plt_stamp64 + ((plt_stamp_counter - plt_stamp) & plt_mask);
     stime = __read_platform_stime(count);
+    if (stamp)
+        *stamp = plt_stamp_counter;
     spin_unlock(&platform_timer_lock);
 
     return stime;
@@ -694,7 +698,7 @@ void cstate_restore_tsc(void)
     if ( boot_cpu_has(X86_FEATURE_NONSTOP_TSC) )
         return;
 
-    write_tsc(stime2tsc(read_platform_stime()));
+    write_tsc(stime2tsc(read_platform_stime(NULL)));
 }
 
 /***************************************************************************
@@ -1005,7 +1009,7 @@ int cpu_frequency_change(u64 freq)
 
     local_irq_disable();
     /* Platform time /first/, as we may be delayed by platform_timer_lock. */
-    t->stime_master_stamp = read_platform_stime();
+    t->stime_master_stamp = read_platform_stime(NULL);
     /* TSC-extrapolated time may be bogus after frequency change. */
     /*t->stime_local_stamp = get_s_time();*/
     t->stime_local_stamp = t->stime_master_stamp;
@@ -1323,7 +1327,7 @@ static void time_calibration_tsc_rendezvous(void *_r)
 
             if ( r->master_stime == 0 )
             {
-                r->master_stime = read_platform_stime();
+                r->master_stime = read_platform_stime(NULL);
                 r->master_tsc_stamp = rdtsc();
             }
             atomic_inc(&r->semaphore);
@@ -1415,7 +1419,7 @@ void init_percpu_time(void)
 
     local_irq_save(flags);
     t->local_tsc_stamp = rdtsc();
-    now = read_platform_stime();
+    now = read_platform_stime(NULL);
     local_irq_restore(flags);
 
     t->stime_master_stamp = now;
-- 
2.1.4