remove sched notifier for cross-cpu migrations

[firefly-linux-kernel-4.4.55.git] / arch / x86 / vdso / vclock_gettime.c

diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index c74436e687bf8984b722efa1a657e1a6a8b47f3b..72074d5284009a35265580a13eaa99e6f11588b4 100644 (file)
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -85,15 +85,18 @@ static notrace cycle_t vread_pvclock(int *mode)
        cycle_t ret;
        u64 last;
        u32 version;
-       u32 migrate_count;
        u8 flags;
        unsigned cpu, cpu1;
 
 
        /*
-        * When looping to get a consistent (time-info, tsc) pair, we
-        * also need to deal with the possibility we can switch vcpus,
-        * so make sure we always re-fetch time-info for the current vcpu.
+        * Note: hypervisor must guarantee that:
+        * 1. cpu ID number maps 1:1 to per-CPU pvclock time info.
+        * 2. that per-CPU pvclock time info is updated if the
+        *    underlying CPU changes.
+        * 3. that version is increased whenever underlying CPU
+        *    changes.
+        *
         */
        do {
                cpu = __getcpu() & VGETCPU_CPU_MASK;
@@ -104,8 +107,6 @@ static notrace cycle_t vread_pvclock(int *mode)
 
                pvti = get_pvti(cpu);
 
-               migrate_count = pvti->migrate_count;
-
                version = __pvclock_read_cycles(&pvti->pvti, &ret, &flags);
 
                /*
@@ -117,8 +118,7 @@ static notrace cycle_t vread_pvclock(int *mode)
                cpu1 = __getcpu() & VGETCPU_CPU_MASK;
        } while (unlikely(cpu != cpu1 ||
                          (pvti->pvti.version & 1) ||
-                         pvti->pvti.version != version ||
-                         pvti->migrate_count != migrate_count));
+                         pvti->pvti.version != version));
 
        if (unlikely(!(flags & PVCLOCK_TSC_STABLE_BIT)))
                *mode = VCLOCK_NONE;