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 B231DC433F5 for ; Mon, 14 Feb 2022 11:22:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350492AbiBNLWU (ORCPT ); Mon, 14 Feb 2022 06:22:20 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:51454 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350665AbiBNLVp (ORCPT ); Mon, 14 Feb 2022 06:21:45 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A174D13D60; Mon, 14 Feb 2022 02:57:48 -0800 (PST) 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 3BC8B60E84; Mon, 14 Feb 2022 10:57:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4E529C340E9; Mon, 14 Feb 2022 10:57:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1644836267; bh=xH46V2BfUDEk4tfDK5AlSlTasUAt3mbtgoN2tyCrJuE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=NY49rm1oYN8KMtEh7BNsW9o9HRKwbmuz+DUYhCUNjfjYjKlX/syU9fRRmA4f1+oig ZNImXBF5GRqIZQghhPYmCucic71XuMLiJrP6RjqIb1+SzBwKeRThx8T95HhuJYwHKD 7/ZqrxEnVPV4dkAA2IUKdjh4GtpePda3FAgvhm9YF4CtGyLNt6v4vjtvZ6xGxjdXX/ +giS63sVuurdMRgDjEIkSdmHs3ZqzdaReEs1/ALdInTmhQsfy4DDSF1vanX7qymwCt gMRwQtsGdHkCBUYZVnz1mrLc3A15gmCzXS5SHBPcpPSrNlKaSnPCpqF6t/IVEnjNbR Gb3zGDlw6xb4Q== Date: Mon, 14 Feb 2022 11:57:44 +0100 From: Frederic Weisbecker To: Yu Liao Cc: paulmck@kernel.org, linux-kernel@vger.kernel.org, liwei391@huawei.com, rcu@vger.kernel.org Subject: Re: Question about nohz and sysidle Message-ID: <20220214105744.GA663287@lothringen> References: 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 Mon, Feb 14, 2022 at 05:40:55PM +0800, Yu Liao wrote: Hi Yu Liao, > > On 2022/2/14 16:28, Yu Liao wrote: > > Hi Frederic, > > > > I'm working on an issue about nohz. When NO_HZ_FULL is enabled, CPU 0 > > handles the timekeeping duty on behalf of all other CPUs, which means > > CPU 0 never stop tick even in sysidle state. This is a powersaving > > issue. > > > > I found your patchset (nohz: Support sysidle) in the below link. > > https://lore.kernel.org/all/1406569056-30217-1-git-send-email-fweisbec@gmail.com/ > > > > But these patches haven't been merged into mainline yet and sysidle > > state detection has been removed by commit fe5ac724d81a (rcu: Remove > > nohz_full full-system-idle state machine) as well. > > > > I tried your patches and it does work, why are we no longer working on > > stopping timekeeping duty when all full dynticks CPUs are idle? Because it was not a priority at that time. There were so many things to handle first (and we are not even done yet) that we postponed that feature until someone ever comes up with powersaving issues on nohz_full. We were waiting for you :) It's possible to unearth this. I think the first step will be to merge the RCU dynticks counters into context tracking, something that was on my queue anyway, and then revive this: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=sysidle.2017.05.11a&id=fe5ac724d81a3c7803e60c2232718f212f3f38d4 Thanks.