linux-kernel - Re: [PATCH tip/core/rcu 11/17] rcu: Bind grace-period kthreads to non-NO_HZ

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Message-ID: <20140711201507.GZ20603@laptop.programming.kicks-ass.net>
Date:	Fri, 11 Jul 2014 22:15:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...two.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	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, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, oleg@...hat.com, sbw@....edu
Subject: Re: [PATCH tip/core/rcu 11/17] rcu: Bind grace-period kthreads to
 non-NO_HZ_FULL CPUs

On Fri, Jul 11, 2014 at 02:05:08PM -0500, Christoph Lameter wrote:
> The use case is pretty straightforward because we are trying to keep as
> much OS noise as possible off most processors. Processor 0 is the
> sacrificial lamb that will be used for all OS processing and hopefully all
> high latency operations will occur there. Processors 1-X have a tick but
> we still try to keep latencies sane. And then there is X-Y where tick is
> off.

So the problem is -- and this isn't too hard to create -- when we
saturate/overload cpu0 with just the housekeeping. At that point it
would be good if we could scale and use multiple housekeepers.
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