Re: [v7 0/8] Reduce cross CPU IPI interference

[Frederic Weisbecker]

On Tue, Feb 14, 2012 at 03:18:03PM +0200, Avi Kivity wrote:
> On 02/10/2012 03:39 AM, Frederic Weisbecker wrote:
> > > 
> > > As long as the code doesn't enter RCU read-side critical sections in
> > > the time between rcu_idle_enter() and rcu_idle_exit(), this should
> > > work fine.
> >
> > This should work fine yeah but further the correctness, I wonder if this
> > is going to be a win.
> >
> > We use rcu_idle_enter() in idle to avoid to keep the tick for RCU. But
> > what about falling into guest mode? I guess the tick is kept there
> > so is it going to be a win in throughput or something to use rcu_idle_enter()?
> 
> We could disable the tick while in guest mode as well.  Interrupts in
> guest mode are even more expensive than interrupts in user mode.

Right, that's definitely something I need to explore with the adaptive tickless
thing.
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