[PATCH 28/40] ARM: sched_clock: provide common infrastructure for sched_clock()

[Nicolas Pitre]

On Fri, 17 Dec 2010, Russell King - ARM Linux wrote:

> On Fri, Dec 17, 2010 at 07:05:54PM +0000, Russell King - ARM Linux wrote:
> > Yes, you're right, it should disable local IRQs across the update.  Thanks
> > for spotting.
> 
> Here's the incremental patch for it.  Note that we can safely explicitly
> disable and re-enable IRQs as the timer subsystem ensures that we will
> always be called with IRQs enabled:
> 
>                         spin_unlock_irq(&base->lock);
>                         call_timer_fn(timer, fn, data);
>                         spin_lock_irq(&base->lock);

Right.  Might be worth putting the above in the commit log too.

With that change you may add:

Reviewed-by: Nicolas Pitre <nicolas.pitre at linaro.org>

> diff --git a/arch/arm/include/asm/sched_clock.h b/arch/arm/include/asm/sched_clock.h
> index 82d4d3f..5643cb0 100644
> --- a/arch/arm/include/asm/sched_clock.h
> +++ b/arch/arm/include/asm/sched_clock.h
> @@ -30,7 +30,7 @@ static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
>   * Atomically update the sched_clock epoch.  Your update callback will
>   * be called from a timer before the counter wraps - read the current
>   * counter value, and call this function to safely move the epochs
> - * forward.
> + * forward.  Only use this from the update callback.
>   */
>  static inline void update_sched_clock(struct clock_data *cd, u32 cyc, u32 mask)
>  {
> @@ -41,11 +41,13 @@ static inline void update_sched_clock(struct clock_data *cd, u32 cyc, u32 mask)
>  	 * Write epoch_cyc and epoch_ns in a way that the update is
>  	 * detectable in cyc_to_fixed_sched_clock().
>  	 */
> +	local_irq_disable();
>  	cd->epoch_cyc = cyc;
>  	smp_wmb();
>  	cd->epoch_ns = ns;
>  	smp_wmb();
>  	cd->epoch_cyc_copy = cyc;
> +	local_irq_enable();
>  }
>  
>  /*
>