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From:   Pavel Tatashin <pasha.tatashin@oracle.com>
To:     steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
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        linux-s390@vger.kernel.org, pasha.tatashin@oracle.com,
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Subject: [PATCH v14 14/25] x86/xen/time: output xen sched_clock time from 0
Date:   Tue, 17 Jul 2018 22:22:00 -0400
Message-Id: <20180718022211.6259-15-pasha.tatashin@oracle.com>
In-Reply-To: <20180718022211.6259-1-pasha.tatashin@oracle.com>
References: <20180718022211.6259-1-pasha.tatashin@oracle.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

It is expected for sched_clock() to output data from 0, when system boots.
Add an offset xen_sched_clock_offset (similarly how it is done in other
hypervisors i.e. kvm_sched_clock_offset) to count sched_clock() from 0,
when time is first initialized.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
---
 arch/x86/xen/time.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 53bb7a8d10b5..25a780d89b7a 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -31,6 +31,8 @@
 /* Xen may fire a timer up to this many ns early */
 #define TIMER_SLOP	100000
 
+static u64 xen_sched_clock_offset __read_mostly;
+
 /* Get the TSC speed from Xen */
 static unsigned long xen_tsc_khz(void)
 {
@@ -57,6 +59,11 @@ static u64 xen_clocksource_get_cycles(struct clocksource *cs)
 	return xen_clocksource_read();
 }
 
+static u64 xen_sched_clock(void)
+{
+	return xen_clocksource_read() - xen_sched_clock_offset;
+}
+
 static void xen_read_wallclock(struct timespec64 *ts)
 {
 	struct shared_info *s = HYPERVISOR_shared_info;
@@ -367,7 +374,7 @@ void xen_timer_resume(void)
 }
 
 static const struct pv_time_ops xen_time_ops __initconst = {
-	.sched_clock = xen_clocksource_read,
+	.sched_clock = xen_sched_clock,
 	.steal_clock = xen_steal_clock,
 };
 
@@ -505,6 +512,7 @@ static void __init xen_time_init(void)
 
 void __init xen_init_time_ops(void)
 {
+	xen_sched_clock_offset = xen_clocksource_read();
 	pv_time_ops = xen_time_ops;
 
 	x86_init.timers.timer_init = xen_time_init;
-- 
2.18.0