linux-kernel - Re: [PATCH][RFC] time: add wait_interruptible_timeout macro to sleep (w. timeout) until wake

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Message-ID: <20100226190100.GQ10145@sci.fi>
Date:	Fri, 26 Feb 2010 21:01:00 +0200
From:	Ville Syrjälä <syrjala@....fi>
To:	Rafał Miłecki <zajec5@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	DRI <dri-devel@...ts.sourceforge.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][RFC] time: add wait_interruptible_timeout macro to
 sleep (w. timeout) until wake_up

On Fri, Feb 26, 2010 at 06:33:57PM +0100, Rafał Miłecki wrote:
> W dniu 26 lutego 2010 17:14 użytkownik Andrew Morton
> <akpm@...ux-foundation.org> napisał:
> > On Fri, 26 Feb 2010 11:38:59 +0100 Rafa Miecki <zajec5@...il.com> wrote:
> >
> >> +#define wait_interruptible_timeout(wq, timeout)
> >>     \
> >> +({                                   \
> >> +    long ret = timeout;                      \
> >> +                                    \
> >> +    DEFINE_WAIT(wait);                      \
> >> +    prepare_to_wait(&wq, &wait, TASK_INTERRUPTIBLE);       \
> >> +    if (!signal_pending(current))                  \
> >> +        ret = schedule_timeout(ret);            \
> >> +    finish_wait(&wq, &wait);                   \
> >> +                                    \
> >> +    ret;                             \
> >> +})
> >
> > It's often a mistake to use signals in-kernel.  Signals are more a
> > userspace thing and it's better to use the lower-level kernel-specific
> > messaging tools in-kernel.  Bear in mind that userspace can
> > independently and asynchronously send, accept and block signals.
> 
> Can you point me to something kernel-level please?
> 
> 
> > Can KMS use wait_event_interruptible_timeout()?
> 
> No. Please check definition of this:
> 
> #define wait_event_interruptible_timeout(wq, condition, timeout)	\
> ({									\
> 	long __ret = timeout;						\
> 	if (!(condition))						\
> 		__wait_event_interruptible_timeout(wq, condition, __ret); \
> 	__ret;								\
> })
> 
> It uses condition there, but that's not a big issue. We just need to
> pass 0 (false) there and it will work so far.

Disabling the condition check doesn't make sense.

You could use a completion.

init_completion(vbl_irq);
enable_vbl_irq();
wait_for_completion(vbl_irq);
disable_vbl_irq();
and call complete(vbl_irq) in the interrupt handler.

The same would of course work with just some flag or counter
and a wait queue. Isn't there already a vbl counter that you could
compare in the condition?

-- 
Ville Syrjälä
syrjala@....fi
http://www.sci.fi/~syrjala/
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