On Sat, Aug 17, 2013 at 08:17:17PM -0700, Josh Triplett wrote:
> On Sat, Aug 17, 2013 at 06:37:46PM -0700, Paul E. McKenney wrote:
> > From: Borislav Petkov <b...@alien8.de>
> >
> > CONFIG_RCU_FAST_NO_HZ can increase grace-period durations by up to
> > a factor of four, which can result in long suspend and resume times.
> > Thus, this commit temporarily switches to expedited grace periods when
> > suspending the box and return to normal settings when resuming.
> >
> > [ paulmck: This also papers over an audio/irq bug, but hopefully that will
> > be fixed soon. ]
> >
> > Signed-off-by: Borislav Petkov <b...@suse.de>
> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
>
> This patch still seems like a hack, and there *ought* to be a better
> general solution to avoid excessive grace-period latency. Nonetheless,
> in the absence of such a solution,
> Reviewed-by: Josh Triplett <j...@joshtriplett.org>
Yeah, I'm not happy about it either but from quickly skimming over what
context we're using rcu_expedited in, the basic requirement for a fix is
for the pm core to be able to tell rcu not to stretch grace periods.
So simply setting a variable is much simpler than switching to calling
all those *_expedited() rcu flavors from the pm notifier when going
down.
Unless Paul has a better idea, of course.
The basic problem here is, however, that you need to temporarily
reconfigure the inner workings of a subsystem because hardware is
performing a power state transition. Unless someone teaches rcu about
power state transitions... :-)
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
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