linux-kernel - Re: [PATCH v2] add function spin_event

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Date:	Mon, 09 Mar 2009 17:06:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Timur Tabi <timur@...escale.com>
Cc:	linux-kernel@...r.kernel.org, rdreier@...co.com,
	jirislaby@...il.com
Subject: Re: [PATCH v2] add function spin_event_timeout()

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@...escale.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) */

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