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Date: Thu, 7 May 2009 10:54:41 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Christoph Lameter <cl@linux.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Alok Kataria <akataria@vmware.com>,
       "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>,
       the arch/x86 maintainers <x86@kernel.org>,
       LKML <linux-kernel@vger.kernel.org>,
       "alan@lxorguk.ukuu.org.uk" <alan@lxorguk.ukuu.org.uk>
Subject: Re: [PATCH] x86: Reduce the default HZ value
Message-ID: <20090507175441.GD6693@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
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On Thu, May 07, 2009 at 01:20:29PM -0400, Christoph Lameter wrote:
> On Thu, 7 May 2009, Peter Zijlstra wrote:
> 
> > Another user is RCU, the grace period is tick driven, growing these
> > ticks by a factor 50 or so might require some tinkering with forced
> > grace periods when we notice our batch queues getting too long.
> 
> One could also schedule RCU via hrtimers with a large fuzz period?

You could, but then you would still have a periodic interrupt introducing
jitter into your HPC workload.  The approach I suggested allows RCU to be
happy with no periodic interrupts on any CPU that has only one runnable
task that is a CPU-bound user-level task (in addition to the idle task,
of course).

							Thanx, Paul