From: Bhavana Nagendra <bnagendr@redhat.com>
Date: Fri, 15 Feb 2008 13:25:30 -0500
Subject: [xen] resync TSC extrapolated frequency
Message-id: 20080215182530.11293.24800.sendpatchset@localhost.localdomain
O-Subject: [RHEL5.2 PATCH 2] Resync TSC extrapolated frequency
Bugzilla: 430938

Resolves BZ 430938

When Xen is notified that CPU frequency has changed, do not trust
the current TSC-extrapolated time when we re-sync.

Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Chris Lalancette <clalance@redhat.com>

diff --git a/arch/x86/time.c b/arch/x86/time.c
index 5587683..ed61d39 100644
--- a/arch/x86/time.c
+++ b/arch/x86/time.c
@@ -733,8 +733,10 @@ int cpu_frequency_change(u64 freq)
     local_irq_disable();
     rdtscll(curr_tsc);
     t->local_tsc_stamp = curr_tsc;
-    t->stime_local_stamp = get_s_time();
     t->stime_master_stamp = read_platform_stime();
+    /* TSC-extrapolated time may be bogus after frequency change. */
+    /*t->stime_local_stamp = get_s_time();*/
+    t->stime_local_stamp = t->stime_master_stamp;
     set_time_scale(&t->tsc_scale, freq);
     local_irq_enable();