Subject: Re: [RFC&PATCH] Alternative RCU implementation
From: Jim Houston <jim.houston@comcast.net>
Reply-To: jim.houston@comcast.net
To: paulmck@us.ibm.com
Cc: linux-kernel@vger.kernel.org, Dipankar Sarma <dipankar@in.ibm.com>,
       Manfred Spraul <manfred@colorfullife.com>,
       Andrew Morton <akpm@osdl.org>,
       William Lee Irwin III <wli@holomorphy.com>,
       Jack Steiner <steiner@sgi.com>, Jesse Barnes <jbarnes@engr.sgi.com>,
       rusty@rustcorp.com.au
In-Reply-To: <20040901035350.GH1241@us.ibm.com>
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On Tue, 2004-08-31 at 23:53, Paul E. McKenney wrote:
> On Mon, Aug 30, 2004 at 11:22:49PM -0400, Jim Houston wrote:
> > On Mon, 2004-08-30 at 14:52, Paul E. McKenney wrote: 
> > > How does the rest of the kernel work with all interrupts to
> > > a particular CPU shut off?  For example, how do you timeslice?
> > 
> > It's a balancing act.  In some cases we just document the
> > missing functionality.  If the local timer is disabled on a cpu,
> > all processes are SCHED_FIFO.  In the case of Posix timers, we
> > move timers to honor the procesor shielding an the process affinity.
> 
> I have to ask...  When you say that you move the timers, you mean that
> non-realtime CPU 1 managers timers for realtime CPU 0, so that CPU 1
> is (effectively) taking CPU 0's timer interrupts?

Hi Paul,

That is part of the idea.  There are lots of timers which we don't
expect to have realtime behavior.

There are also services like Posix timers and nanosleep() where we want
very predictable behavior.  If a process does a nanosleep(), we queue
that timer on the local cpu.  If process affinity is changed, we will
move the timer to a cpu where the process is allowed to run.

We have separate queues for high resolution timers.  If the local queue
is empty, we shutdown the timer.

Jim Houston - Concurrent Computer Corp.


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