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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Joel Fernandes <joel@joelfernandes.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, Boqun Feng <boqun.feng@gmail.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>
Subject: Re: RCU vs NOHZ
Date: Fri, 30 Sep 2022 07:48:12 -0700	[thread overview]
Message-ID: <20220930144812.GA1801669@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <20220929195641.GZ4196@paulmck-ThinkPad-P17-Gen-1>

On Thu, Sep 29, 2022 at 12:56:41PM -0700, Paul E. McKenney wrote:
> On Thu, Sep 29, 2022 at 09:08:42PM +0200, Peter Zijlstra wrote:
> > On Thu, Sep 29, 2022 at 09:36:24AM -0700, Paul E. McKenney wrote:
> > 
> > > > How has this been tried; and why did the energy cost go up? Is this
> > > > because the offload thread ends up waking up the CPU we just put to
> > > > sleep?
> > > 
> > > Because doing the additional work consumes energy.  I am not clear on
> > > exactly what you are asking for here, given the limitations of the tools
> > > that measure energy consumption.
> > 
> > What additional work? Splicing the cpu pending list onto another list
> > with or without atomic op barely qualifies for work. The main point is
> > making sure the pending list isn't in the way of going (deep) idle.
> 
> Very good.  Send a patch.
> 
> After some time, its successor might correctly handle lock/memory
> contention, CPU hotplug, presumed upcoming runtime changes in CPUs'
> housekeeping status, frequent idle entry/exit, grace period begin/end,
> quiet embedded systems, and so on.
> 
> Then we can see if it actually reduces power consumption.

Another approach is to runtime-offload CPUs that have been mostly idle,
and switch back to deoffloaded during busy periods.

							Thanx, Paul

  reply	other threads:[~2022-09-30 14:48 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-15  8:39 RCU vs NOHZ Peter Zijlstra
2022-09-15 15:37 ` Joel Fernandes
2022-09-15 16:06 ` Paul E. McKenney
2022-09-15 18:50   ` Peter Zijlstra
2022-09-15 19:14     ` Paul E. McKenney
2022-09-15 22:30       ` Peter Zijlstra
2022-09-16  3:40         ` Joel Fernandes
2022-09-16  7:58         ` Paul E. McKenney
2022-09-16  9:20           ` Peter Zijlstra
2022-09-16 18:11             ` Joel Fernandes
2022-09-17 13:35               ` Peter Zijlstra
2022-09-17 13:52                 ` Joel Fernandes
2022-09-17 14:28                   ` Paul E. McKenney
2022-09-17 14:25             ` Paul E. McKenney
2022-09-21 21:36               ` Paul E. McKenney
2022-09-23 15:12                 ` Joel Fernandes
2022-09-23 16:01                   ` Paul E. McKenney
2022-09-23 17:47                     ` Joel Fernandes
2022-09-23 18:15                       ` Paul E. McKenney
2022-09-29 11:06                 ` Peter Zijlstra
2022-09-29 10:55               ` Peter Zijlstra
2022-09-29 15:20                 ` Paul E. McKenney
2022-09-29 15:46                   ` Paul E. McKenney
2022-09-29 16:05                     ` Joel Fernandes
2022-09-29 16:23                     ` Peter Zijlstra
2022-09-29 16:42                       ` Paul E. McKenney
2022-09-29 19:01                         ` Peter Zijlstra
2022-09-29 19:52                           ` Paul E. McKenney
2022-09-29 16:18                   ` Peter Zijlstra
2022-09-29 16:36                     ` Paul E. McKenney
2022-09-29 19:08                       ` Peter Zijlstra
2022-09-29 19:56                         ` Paul E. McKenney
2022-09-30 14:48                           ` Paul E. McKenney [this message]
2022-09-23 19:47 Joel Fernandes

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