On 07/11/2018 08:04 PM, Pavel Tatashin wrote:
> 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@xxxxxxxxxx>
> ---
> 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 2ad61bf896d6..3c6f3d603373 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;
> +}
Should other invocations of xen_clocksource_read() also be offset?
-boris
> +
> 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;
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