From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E70F9C433F5 for ; Thu, 29 Sep 2022 19:56:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229576AbiI2T4r (ORCPT ); Thu, 29 Sep 2022 15:56:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42356 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229484AbiI2T4o (ORCPT ); Thu, 29 Sep 2022 15:56:44 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C06F41EC9B2 for ; Thu, 29 Sep 2022 12:56:43 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B66296216A for ; Thu, 29 Sep 2022 19:56:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 25813C433C1; Thu, 29 Sep 2022 19:56:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664481402; bh=nppm+sLoKjXXKAFW+4L5wobI8BPs7jkgM6v5WRbgCJM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=OsnKtNeihCRcHtHXa3pG5UO46PjSYEGQ6Eg4ZNcXYfnLZtD/7PJMEajaZvSSszvQD PspL4PZEiN9bLkuPRe/Yp5qv9v3JjoAjVu67JYRu+7Avb2ziEjw9L5iwKk1R5HRkzy zSOM1AMK7qly2qWR8WW158a+JrgmRbkFwGaPDbozv0yMoyiw/iT3z3+yBcD4hqHqrh AxG/2qOmcHwjEygwHHpVX6pac4+BB+sQ7JFAYw1ZrbCkoYKBJiZSv6a92YV9STZIPd I8AB7XDTac8/H7qHrJa6ZaJLYybJu/caHz3YxfrYqelcgM0XLmBzCwzhuELxS0xawG h+SV+SQhaTwTQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id C21855C0AC7; Thu, 29 Sep 2022 12:56:41 -0700 (PDT) Date: Thu, 29 Sep 2022 12:56:41 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Joel Fernandes , Frederic Weisbecker , Thomas Gleixner , linux-kernel@vger.kernel.org, Boqun Feng , "Rafael J. Wysocki" Subject: Re: RCU vs NOHZ Message-ID: <20220929195641.GZ4196@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220915191427.GC246308@paulmck-ThinkPad-P17-Gen-1> <20220916075817.GE246308@paulmck-ThinkPad-P17-Gen-1> <20220917142508.GF246308@paulmck-ThinkPad-P17-Gen-1> <20220929152044.GE4196@paulmck-ThinkPad-P17-Gen-1> <20220929163624.GN4196@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanx, Paul