From: Uladzislau Rezki <urezki@gmail.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: joel@joelfernandes.org, rcu@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: Energy-efficiency options within RCU
Date: Thu, 10 Dec 2020 20:23:58 +0100 [thread overview]
Message-ID: <20201210192358.GA2365@pc638.lan> (raw)
In-Reply-To: <20201210183737.GA12900@paulmck-ThinkPad-P72>
Hello, Paul.
[Dropping CC]
> Hello, Joel,
>
> In case you are -seriously- interested... ;-)
>
> Thanx, Paul
>
> rcu_nocbs=
>
> Adding a CPU to this list offloads RCU callback invocation from
> that CPU's softirq handler to a kthread. In big.LITTLE systems,
> this kthread can be placed on a LITTLE CPU, which has been
> demonstrated to save significant energy in benchmarks.
> http://www.rdrop.com/users/paulmck/realtime/paper/AMPenergy.2013.04.19a.pdf
>
I have checked our config. We do use rcu_nocbs=0-7 as kthreads but what
i see those threads are not bound to 0-3 CPUs. In our case it is little
cluster. I think i should check and run some test cases regarding power
savings if i pin all threads to little cluster.
> rcutree.rcu_idle_gp_delay= (Only CONFIG_RCU_FAST_NO_HZ=y kernels.)
>
> This defaults to four jiffies on the theory that grace periods
> tend to last about that long. If grace periods tend to take
> longer, then it makes a lot of sense to increase this. And maybe
> battery-powered devices would rather have it be about 2x or 3x
> the expected grace-period duration, who knows?
>
> I would keep it to a power of two, but the code should work with
> other numbers. Except that I don't know that this has ever been
> tested. ;-)
>
Same here. We do use it.
--
Vlad Rezki
next prev parent reply other threads:[~2020-12-10 19:26 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-10 18:37 Energy-efficiency options within RCU Paul E. McKenney
2020-12-10 19:23 ` Uladzislau Rezki [this message]
2020-12-14 18:12 ` Joel Fernandes
2020-12-14 19:02 ` Paul E. McKenney
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