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    Subject[PATCH/RFC] replace get_scheduled_cycles with sched_clock paravirt_op
    Subject: Add a sched_clock paravirt_op

    The tsc-based get_scheduled_cycles interface is not a good match for
    Xen's runstate accounting, which reports everything in nanoseconds.

    This patch replaces this interface with a sched_clock interface, which
    matches both Xen and VMI's requirements.

    In order to do this, we:
    1. replace get_scheduled_cycles with sched_clock
    2. hoist cycles_2_ns into a common header
    3. update vmi accordingly

    One thing to note: because sched_clock is implemented as a weak function in
    kernel/sched.c, we must define a real function in order to override this weak
    binding. This means the usual paravirt_ops technique of using an inline
    function won't work in this case.

    Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
    Cc: Zachary Amsden <zach@vmware.com>
    Cc: Dan Hecht <dhecht@vmware.com>
    Cc: john stultz <johnstul@us.ibm.com>

    ---
    arch/i386/kernel/paravirt.c | 2 +-
    arch/i386/kernel/tsc.c | 23 +++++++++++++++--------
    arch/i386/kernel/vmi.c | 2 +-
    arch/i386/kernel/vmitime.c | 6 +++---
    include/asm-i386/paravirt.h | 7 +++++--
    include/asm-i386/timer.h | 32 +++++++++++++++++++++++++++++++-
    include/asm-i386/vmi_time.h | 2 +-
    7 files changed, 57 insertions(+), 17 deletions(-)

    ===================================================================
    --- a/arch/i386/kernel/paravirt.c
    +++ b/arch/i386/kernel/paravirt.c
    @@ -552,7 +552,7 @@ struct paravirt_ops paravirt_ops = {
    .write_msr = native_write_msr,
    .read_tsc = native_read_tsc,
    .read_pmc = native_read_pmc,
    - .get_scheduled_cycles = native_read_tsc,
    + .sched_clock = native_sched_clock,
    .get_cpu_khz = native_calculate_cpu_khz,
    .load_tr_desc = native_load_tr_desc,
    .set_ldt = native_set_ldt,
    ===================================================================
    --- a/arch/i386/kernel/tsc.c
    +++ b/arch/i386/kernel/tsc.c
    @@ -81,7 +81,7 @@ static inline int check_tsc_unstable(voi
    *
    * -johnstul@us.ibm.com "math is hard, lets go shopping!"
    */
    -static unsigned long cyc2ns_scale __read_mostly;
    +unsigned long cyc2ns_scale __read_mostly;

    #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */

    @@ -90,15 +90,10 @@ static inline void set_cyc2ns_scale(unsi
    cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
    }

    -static inline unsigned long long cycles_2_ns(unsigned long long cyc)
    -{
    - return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
    -}
    -
    /*
    * Scheduler clock - returns current time in nanosec units.
    */
    -unsigned long long sched_clock(void)
    +unsigned long long native_sched_clock(void)
    {
    unsigned long long this_offset;

    @@ -110,11 +105,23 @@ unsigned long long sched_clock(void)
    return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);

    /* read the Time Stamp Counter: */
    - get_scheduled_cycles(this_offset);
    + rdtscll(this_offset);

    /* return the value in ns */
    return cycles_2_ns(this_offset);
    }
    +
    +/* We need to define a real function for sched_clock, to override the
    + weak default version */
    +#ifdef CONFIG_PARAVIRT
    +unsigned long long sched_clock(void)
    +{
    + return paravirt_sched_clock();
    +}
    +#else
    +unsigned long long sched_clock(void)
    + __attribute__((alias("native_sched_clock")));
    +#endif

    unsigned long native_calculate_cpu_khz(void)
    {
    ===================================================================
    --- a/arch/i386/kernel/vmi.c
    +++ b/arch/i386/kernel/vmi.c
    @@ -871,7 +871,7 @@ static inline int __init activate_vmi(vo
    paravirt_ops.setup_boot_clock = vmi_timer_setup_boot_alarm;
    paravirt_ops.setup_secondary_clock = vmi_timer_setup_secondary_alarm;
    #endif
    - paravirt_ops.get_scheduled_cycles = vmi_get_sched_cycles;
    + paravirt_ops.sched_clock = vmi_sched_clock;
    paravirt_ops.get_cpu_khz = vmi_cpu_khz;

    /* We have true wallclock functions; disable CMOS clock sync */
    ===================================================================
    --- a/arch/i386/kernel/vmitime.c
    +++ b/arch/i386/kernel/vmitime.c
    @@ -163,9 +163,9 @@ int vmi_set_wallclock(unsigned long now)
    return -1;
    }

    -unsigned long long vmi_get_sched_cycles(void)
    -{
    - return read_available_cycles();
    +unsigned long long vmi_sched_clock(void)
    +{
    + return cycles_2_ns(read_available_cycles());
    }

    unsigned long vmi_cpu_khz(void)
    ===================================================================
    --- a/include/asm-i386/paravirt.h
    +++ b/include/asm-i386/paravirt.h
    @@ -92,7 +92,7 @@ struct paravirt_ops

    u64 (*read_tsc)(void);
    u64 (*read_pmc)(void);
    - u64 (*get_scheduled_cycles)(void);
    + unsigned long long (*sched_clock)(void);
    unsigned long (*get_cpu_khz)(void);

    void (*load_tr_desc)(void);
    @@ -549,7 +549,10 @@ static inline void halt(void)

    #define rdtscll(val) (val = PVOP_CALL0(u64, read_tsc))

    -#define get_scheduled_cycles(val) (val = paravirt_ops.get_scheduled_cycles())
    +static inline unsigned long long paravirt_sched_clock(void)
    +{
    + return PVOP_CALL0(unsigned long long, sched_clock);
    +}
    #define calculate_cpu_khz() (paravirt_ops.get_cpu_khz())

    #define write_tsc(val1,val2) wrmsr(0x10, val1, val2)
    ===================================================================
    --- a/include/asm-i386/timer.h
    +++ b/include/asm-i386/timer.h
    @@ -17,8 +17,38 @@ extern int recalibrate_cpu_khz(void);
    extern int recalibrate_cpu_khz(void);

    #ifndef CONFIG_PARAVIRT
    -#define get_scheduled_cycles(val) rdtscll(val)
    #define calculate_cpu_khz() native_calculate_cpu_khz()
    #endif

    +/* Accellerators for sched_clock()
    + * convert from cycles(64bits) => nanoseconds (64bits)
    + * basic equation:
    + * ns = cycles / (freq / ns_per_sec)
    + * ns = cycles * (ns_per_sec / freq)
    + * ns = cycles * (10^9 / (cpu_khz * 10^3))
    + * ns = cycles * (10^6 / cpu_khz)
    + *
    + * Then we use scaling math (suggested by george@mvista.com) to get:
    + * ns = cycles * (10^6 * SC / cpu_khz) / SC
    + * ns = cycles * cyc2ns_scale / SC
    + *
    + * And since SC is a constant power of two, we can convert the div
    + * into a shift.
    + *
    + * We can use khz divisor instead of mhz to keep a better percision, since
    + * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
    + * (mathieu.desnoyers@polymtl.ca)
    + *
    + * -johnstul@us.ibm.com "math is hard, lets go shopping!"
    + */
    +extern unsigned long cyc2ns_scale __read_mostly;
    +
    +#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
    +
    +static inline unsigned long long cycles_2_ns(unsigned long long cyc)
    +{
    + return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
    +}
    +
    +
    #endif
    ===================================================================
    --- a/include/asm-i386/vmi_time.h
    +++ b/include/asm-i386/vmi_time.h
    @@ -49,7 +49,7 @@ extern void __init vmi_time_init(void);
    extern void __init vmi_time_init(void);
    extern unsigned long vmi_get_wallclock(void);
    extern int vmi_set_wallclock(unsigned long now);
    -extern unsigned long long vmi_get_sched_cycles(void);
    +extern unsigned long long vmi_sched_clock(void);
    extern unsigned long vmi_cpu_khz(void);

    #ifdef CONFIG_X86_LOCAL_APIC
    -
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