linux-kernel - Re: [PATCH tip/core/rcu 1/2] rcu: Parallelize and economize NOCB kthread wakeups

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Message-ID: <20140824032339.GK2663@linux.vnet.ibm.com>
Date:	Sat, 23 Aug 2014 20:23:39 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Pranith Kumar <pranith@...ech.edu>
Cc:	Amit Shah <amit.shah@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>, dvhart@...ux.intel.com,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Silas Boyd-Wickizer <sbw@....edu>
Subject: Re: [PATCH tip/core/rcu 1/2] rcu: Parallelize and economize NOCB
 kthread wakeups

On Sat, Aug 23, 2014 at 08:26:10PM -0400, Pranith Kumar wrote:
> On Sat, Aug 23, 2014 at 12:51 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > It might well!  Another possibility is that the early_initcall function
> > doing the synchronize_rcu() is happening before the early_initcall
> > creating the RCU grace-period kthreads.
> >
> > Seems like we need to close both holes.  Let's see how your patch works
> > for Amit, and I am testing a patch for the possible early_initcall
> > ordering issue.
> 
> I checked the init call which is calling synchronize_rcu():
> subsys_initcall(pm_sysrq_init); this is being called after
> early_initcall.
> 
> The order of initcalls is early, core, postcore, arch, subsys, fs,
> device, late. So I guess that is ok.
> 
> I wonder why it was not showing up in 12.04. I have a dual boot. Will
> test it out and see if I can find something.

Me, I am wondering about 7,000 callbacks being registered during early
boot time.  ;-)

							Thanx, Paul

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