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    Subject[tip:x86/timers] x86/xen/time: Output xen sched_clock time from 0
    Commit-ID:  38669ba205d178d2d38bfd194a196d65a44d5af2
    Gitweb: https://git.kernel.org/tip/38669ba205d178d2d38bfd194a196d65a44d5af2
    Author: Pavel Tatashin <pasha.tatashin@oracle.com>
    AuthorDate: Thu, 19 Jul 2018 16:55:32 -0400
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Fri, 20 Jul 2018 00:02:40 +0200

    x86/xen/time: Output xen sched_clock time from 0

    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>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: steven.sistare@oracle.com
    Cc: daniel.m.jordan@oracle.com
    Cc: linux@armlinux.org.uk
    Cc: schwidefsky@de.ibm.com
    Cc: heiko.carstens@de.ibm.com
    Cc: john.stultz@linaro.org
    Cc: sboyd@codeaurora.org
    Cc: hpa@zytor.com
    Cc: douly.fnst@cn.fujitsu.com
    Cc: peterz@infradead.org
    Cc: prarit@redhat.com
    Cc: feng.tang@intel.com
    Cc: pmladek@suse.com
    Cc: gnomes@lxorguk.ukuu.org.uk
    Cc: linux-s390@vger.kernel.org
    Cc: boris.ostrovsky@oracle.com
    Cc: jgross@suse.com
    Cc: pbonzini@redhat.com
    Link: https://lkml.kernel.org/r/20180719205545.16512-14-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;
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