Re: [PATCH 6/7] clocksource: Add Pistachio clocksource-only driver

[Thomas Gleixner]

On Thu, 21 May 2015, Ezequiel Garcia wrote:
> +static cycle_t clocksource_read_cycles(struct clocksource *cs)
> +{
> +	u32 counter, overflw;
> +	unsigned long flags;
> +
> +	raw_spin_lock_irqsave(&lock, flags);

Hmm. Is that lock really necessary to read that counter? The
clocksource is global. And if its actually used for timekeeping, the
lock can get heavy contended.

> +	overflw = gpt_readl(TIMER_CURRENT_OVERFLOW_VALUE, 0);
> +	counter = gpt_readl(TIMER_CURRENT_VALUE, 0);
> +	raw_spin_unlock_irqrestore(&lock, flags);
> +
> +	return ~(cycle_t)counter;
> +}

Thanks,

	tglx
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