remove sched notifier for cross-cpu migrations

Linux as a guest on KVM hypervisor, the only user of the pvclock
vsyscall interface, does not require notification on task migration
because:

1. cpu ID number maps 1:1 to per-CPU pvclock time info.
2. per-CPU pvclock time info is updated if the
   underlying CPU changes.
3. that version is increased whenever underlying CPU
   changes.

Which is sufficient to guarantee nanoseconds counter
is calculated properly.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 0 insertions, 44 deletions

diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 2cb9470ea85b..a16bae3f83b3 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -128,46 +128,7 @@ void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
         set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
 }
 
-static struct pvclock_vsyscall_time_info *pvclock_vdso_info;
-
-static struct pvclock_vsyscall_time_info *
-pvclock_get_vsyscall_user_time_info(int cpu)
-{
-        if (!pvclock_vdso_info) {
-                BUG();
-                return NULL;
-        }
-
-        return &pvclock_vdso_info[cpu];
-}
-
-struct pvclock_vcpu_time_info *pvclock_get_vsyscall_time_info(int cpu)
-{
-        return &pvclock_get_vsyscall_user_time_info(cpu)->pvti;
-}
-
 #ifdef CONFIG_X86_64
-static int pvclock_task_migrate(struct notifier_block *nb, unsigned long l,
-                                void *v)
-{
-        struct task_migration_notifier *mn = v;
-        struct pvclock_vsyscall_time_info *pvti;
-
-        pvti = pvclock_get_vsyscall_user_time_info(mn->from_cpu);
-
-        /* this is NULL when pvclock vsyscall is not initialized */
-        if (unlikely(pvti == NULL))
-                return NOTIFY_DONE;
-
-        pvti->migrate_count++;
-
-        return NOTIFY_DONE;
-}
-
-static struct notifier_block pvclock_migrate = {
-        .notifier_call = pvclock_task_migrate,
-};
-
 /*
  * Initialize the generic pvclock vsyscall state.  This will allocate
  * a/some page(s) for the per-vcpu pvclock information, set up a
@@ -181,17 +142,12 @@ int __init pvclock_init_vsyscall(struct pvclock_vsyscall_time_info *i,
 
         WARN_ON (size != PVCLOCK_VSYSCALL_NR_PAGES*PAGE_SIZE);
 
-        pvclock_vdso_info = i;
-
         for (idx = 0; idx <= (PVCLOCK_FIXMAP_END-PVCLOCK_FIXMAP_BEGIN); idx++) {
                 __set_fixmap(PVCLOCK_FIXMAP_BEGIN + idx,
                              __pa(i) + (idx*PAGE_SIZE),
                              PAGE_KERNEL_VVAR);
         }
 
-
-        register_task_migration_notifier(&pvclock_migrate);
-
         return 0;
 }
 #endif