Re: [PATCH v2] add function spin_event_timeout()

Peter Zijlstra
2009-03-09T16:06:33Z

On Mon, 2009-03-09 at 10:18 -0500, Timur Tabi wrote:
> The function spin_event_timeout() takes a condition and timeout value
> (in jiffies) as parameters. It spins until either the condition is true
> or the timeout expires. It returns non-zero if the condition is true,
> zero otherwise.

This changelog utterly fails to justify this interface. And to me it
seems a rather bad one. Why would we ever be wanting to spin in order of
jiffies?

> Signed-off-by: Timur Tabi <timur@freescale.com>
> ---
>
> v2: changes based on feedback
>
> include/linux/delay.h | 22 ++++++++++++++++++++++
> 1 files changed, 22 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/delay.h b/include/linux/delay.h
> index fd832c6..235ca25 100644
> --- a/include/linux/delay.h
> +++ b/include/linux/delay.h
> @@ -51,4 +51,26 @@ static inline void ssleep(unsigned int seconds)
> msleep(seconds * 1000);
> }
>
> +/**
> + * spin_event_timeout - spin until a condition gets true or a timeout elapses
> + * @condition: a C expression for the event to wait for
> + * @timeout: timeout, in jiffies
> + *
> + * The process spins until the @condition evaluates to true or the @timeout
> + * elapses.
> + *
> + * The function returns non-zero if the @condition evaluated to true, or
> + * zero if the @timeout elapsed. If both occurs (e.g. the loop was
> + * pre-empted and the @condition became true in the meantime, but when the
> + * loop resumed the @timeout had already elapsed), then non-zero will be
> + * returned.
> + */
> +#define spin_event_timeout(condition, timeout) \
> +({ \
> + unsigned long __timeout = jiffies + (timeout); \
> + while (!(condition) && time_before(jiffies, __timeout)) \
> + cpu_relax(); \
> + (condition); \
> +})
> +
> #endif /* defined(_LINUX_DELAY_H) */