Re: [PATCH] Extend mwait idle to optimize away CAL and RESinterrupts to an idle CPU -v1

[Paul E. McKenney]

On Fri, Feb 24, 2012 at 01:41:50PM +0800, Yong Zhang wrote:
> On Thu, Feb 23, 2012 at 11:34:11AM -0800, Venki Pallipadi wrote:
> > On Thu, Feb 23, 2012 at 1:30 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > > Why not scheduler_ipi()?
> > 
> > Was trying to avoid irq_enter/exit. As the work here is done in idle
> > thread context, I though we could avoid enter/exit. 
> 
> It seems we could not.
> At least RCU need it, see commit c5d753a55, otherwise we will get
> warning like 'RCU used illegally from extended quiescent state!'

If the use is tracing, then Steven Rostedt's patchset plus use of his
_rcuidle() tracing variants handles this:

	https://lkml.org/lkml/2012/2/7/231

If this is instead algorithmic use of RCU, a set of patches I have queued
up for 3.4 will be required.

							Thanx, Paul

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