Re: Fw: [RFC] Strange code in cpu_idle()

[Stephen Rothwell <sfr@canb.auug.org.au>]

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Hi Paul,

On Sat, 4 Dec 2004 16:45:57 -0800 "Paul E. McKenney" <paulmck@us.ibm.com> wrote:
>
> OK, I believe I found the other end of this:
> 
> static void __exit apm_exit(void)
> {
> 	int	error;
> 
> 	if (set_pm_idle) {
> 		pm_idle = original_pm_idle;
> 		/*
> 		 * We are about to unload the current idle thread pm callback
> 		 * (pm_idle), Wait for all processors to update cached/local
> 		 * copies of pm_idle before proceeding.
> 		 */
> 		synchronize_kernel();
> 	}
> 
> Unfortunately, the idle loop is a quiescent state, so it is
> possible for synchronize_kernel() to return before the idle threads
> have returned.  So I don't believe RCU is useful here.  One other
> approach would be to keep a cpu mask, in which apm_exit() sets all
> bits, and pm_idle() clears its CPU's bit only if it is set.
> Then apm_exit() could wait for all CPU's bits to clear.
> 
> There is probably a better way to do this, but that is what comes
> to mind immediately.
> 
> Thoughts?

None, sorry :-)

I don't even remember that piece of code going in (I certainly didn't
write it), though I can see what it was trying to do.

-- 
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au
http://www.canb.auug.org.au/~sfr/

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