linux-kernel - Re: [PATCH tip/core/rcu] Reduce overhead of cond

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Message-ID: <20140623164529.GE4603@linux.vnet.ibm.com>
Date:	Mon, 23 Jun 2014 09:45:29 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...two.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, dave.hansen@...el.com,
	ak@...ux.intel.com, umgwanakikbuti@...il.com
Subject: Re: [PATCH tip/core/rcu] Reduce overhead of cond_resched() checks
 for RCU

On Mon, Jun 23, 2014 at 08:51:08AM -0500, Christoph Lameter wrote:
> On Mon, 23 Jun 2014, Peter Zijlstra wrote:
> 
> > On the topic of these threads; I recently noticed RCU grew a metric ton
> > of them, I found some 75 rcu kthreads on my box, wth up with that?
> 
> Would kworker threads work for rcu? That would also avoid the shifting
> around of RCU threads for NOHZ configurations (which seems to have to be
> done manually right now). The kworker subsystem work that allows
> restriction to non NOHZ hardware threads would then also allow the
> shifting of the rcu threads which would simplify the whole endeavor.

Short term, I am planning to use a different method to automate the
binding of the rcuo kthreads to housekeeping CPUs, but longer term,
it might well make a lot of sense to move to workqueues and the kworker
threads.

							Thanx, Paul

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