linux-kernel - Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi

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Date:	Wed, 6 Jun 2012 07:44:17 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"Luck, Tony" <tony.luck@...el.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...e.hu>, H Peter Anvin <hpa@...or.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Mallick, Asit K" <asit.k.mallick@...el.com>,
	Arjan Dan De Ven <arjan@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	x86 <x86@...nel.org>, linux-pm <linux-pm@...r.kernel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi

On Wed, Jun 06, 2012 at 10:42:55AM +0200, Peter Zijlstra wrote:
> On Tue, 2012-06-05 at 15:12 -0700, Paul E. McKenney wrote:
> > > RCU has similar nasties.
> > 
> > I am working to rid RCU of this sort of thing.  I have rcu_barrier() so
> > that it avoids messing with CPUs that don't have callbacks, which will
> > be almost all of the idle CPUs, especially for CONFIG_RCU_FAST_NO_HZ=y.
> > I believe that I have also removed all of RCU's dependencies on CPU
> > hotplug's using kstopmachine, though Murphy would say otherwise.
> > 
> > I still need to fix up synchronize_sched_expedited(), but that is on
> > the list.  I considered getting rid of this one, but I am probably going
> > to have to make synchronize_sched() map to it during boot time to keep
> > the boot-speed demons satisfied. 
> 
> Not the point really. Its perfectly fine for applications in an
> 'isolated' set to use system calls, hence they get to participate in RCU
> state.
> 
> I don't think the isolation means userspace while(1) applications is
> interesting. Sure, some people do this, and we should dtrt for them, but
> the far more interesting case is 'regular' applications that do use
> system calls.

OK, I will bite.  What are the semantics/properties for your isolated set?

							Thanx, Paul

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