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    SubjectRe: Fwd: Commit 76a2a6ee8a0660a29127f05989ac59ae1ce865fa breaks PXA270 (at least)?
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    Date
    On Thu, 2008-07-31 at 23:37 +0200, Ingo Molnar wrote:
    > * Andrew Morton <akpm@linux-foundation.org> wrote:
    >
    > > On Tue, 29 Jul 2008 23:31:05 +0100
    > > Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:
    > >
    > > > But then some bright spark thought it would be a good idea to get
    > > > rid of printk_clock().
    > >
    > > <does git-log, searches for printk_clock>
    >
    > i think this is a fresh regression via the introduction of
    > kernel/sched_clock.c. We lost the (known) early-init behavior of
    > cpu_clock() in the !UNSTABLE_SCHED_CLOCK case. The fix would be to
    > restore that, not to reintroduce printk_clock().
    >
    > Peter, any ideas?

    How about something like this, it builds an atificial delay, exactly
    like we already have for the HAVE_UNSTABLE_SCHED_CLOCK case.

    This keeps cpu_clock() 0 until after sched_clock_init().

    Russell, Bill, is this sufficient?

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 1b26ed2..d13264b 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -1550,16 +1550,10 @@ static inline int set_cpus_allowed(struct task_struct *p, cpumask_t new_mask)

    extern unsigned long long sched_clock(void);

    -#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
    -static inline void sched_clock_init(void)
    -{
    -}
    -
    -static inline u64 sched_clock_cpu(int cpu)
    -{
    - return sched_clock();
    -}
    +extern void sched_clock_init(void);
    +extern u64 sched_clock_cpu(int cpu);

    +#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
    static inline void sched_clock_tick(void)
    {
    }
    @@ -1583,8 +1577,6 @@ static inline void sched_clock_tick_start(int cpu)
    #endif

    #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
    -extern void sched_clock_init(void);
    -extern u64 sched_clock_cpu(int cpu);
    extern void sched_clock_tick(void);
    extern void sched_clock_idle_sleep_event(void);
    extern void sched_clock_idle_wakeup_event(u64 delta_ns);
    diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
    index 22ed55d..a804582 100644
    --- a/kernel/sched_clock.c
    +++ b/kernel/sched_clock.c
    @@ -32,6 +32,7 @@
    #include <linux/ktime.h>
    #include <linux/module.h>

    +static __read_mostly int sched_clock_running;

    #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

    @@ -71,8 +72,6 @@ static inline struct sched_clock_data *cpu_sdc(int cpu)
    return &per_cpu(sched_clock_data, cpu);
    }

    -static __read_mostly int sched_clock_running;
    -
    void sched_clock_init(void)
    {
    u64 ktime_now = ktime_to_ns(ktime_get());
    @@ -319,6 +318,21 @@ void sched_clock_idle_wakeup_event(u64 delta_ns)
    }
    EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);

    +#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
    +
    +void sched_clock_init(void)
    +{
    + sched_clock_running = 1;
    +}
    +
    +u64 sched_clock_cpu(int cpu)
    +{
    + if (unlikely(!sched_clock_running))
    + return 0;
    +
    + return sched_clock();
    +}
    +
    #endif

    /*



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