linux-kernel - Re: + do_wait-wakeup-optimization.patch added to -mm tree

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Message-ID: <20081204152601.GB8816@redhat.com>
Date:	Thu, 4 Dec 2008 16:26:01 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu, rnalumasu@...il.com
Subject: Re: + do_wait-wakeup-optimization.patch added to -mm tree

On 11/23, Roland McGrath wrote:
>
> > > +static int do_wait_wake_function(wait_queue_t *curr, unsigned mode, int sync,
> > > +				 void *key)
> > > +{
> > > +	struct task_struct *task = current;
> >
> > I think we can fix (and simplify) this code if we change __wake_up_parent(),
> > it should call __wake_up(key => p), so we can do
> >
> > 	struct task_struct *task = key;
>
> I don't see an exposed __wake_up* variant that both passes a "key" pointer
> through and does "sync".  For __wake_up_parent, "sync" is quite desireable.

Well, yes... and __wake_up_common() is static. Perhaps we can make a new
helper. I must admit, I don't understand what "sync" actually means nowadays.

> > > +	if (!needs_wakeup(task, w))
> > > +		return 0;
> > > +
> > > +	return default_wake_function(curr, mode, sync, key);
> >
> > perhaps autoremove_wake_function() makes more sense.
>
> Why?  The do_wait loop will have to go through again and still might just
> sleep again.  The explicit remove at the end of do_wait seems fine to me.

Yes, yes, I was wrong. I forgot about "repeat:" in do_wait().

Oleg.

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