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Subject[PATCH v15 13/26] x86/xen/time: output xen sched_clock time from 0
Date
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 | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 53bb7a8d10b5..c84f1e039d84 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;
@@ -546,6 +554,7 @@ void __init xen_hvm_init_time_ops(void)
return;
}

+ xen_sched_clock_offset = xen_clocksource_read();
pv_time_ops = xen_time_ops;
x86_init.timers.setup_percpu_clockev = xen_time_init;
x86_cpuinit.setup_percpu_clockev = xen_hvm_setup_cpu_clockevents;
--
2.18.0
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