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 X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BF875C4727C for ; Fri, 25 Sep 2020 22:55:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 71B70208B6 for ; Fri, 25 Sep 2020 22:55:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="NHJmHf2F"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="GqqH+xCt" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729217AbgIYWzP (ORCPT ); Fri, 25 Sep 2020 18:55:15 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:58988 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727067AbgIYWzP (ORCPT ); Fri, 25 Sep 2020 18:55:15 -0400 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1601074512; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Obvuz1/Dj7IREACiXdEW9/bPBhlEoJrZlnsY+GA+QsE=; b=NHJmHf2F/2L+Lr06oq/aLPShHvQK+jsH5M+NtrE12xin+1ngh9rlfeupCo+0jj8oCTyWCP 5NMK4H5Mf+WmZ3h5Qa/dBmI94v1M2w6r42T2M8x6A8wUIxT2flHjLBQRs3++5zVhvsuobD /1ZZgVuVuPEC5pIDGit+u34uO2FjPerJItpKi4jGUXHa2Xb+4LogMX6HXgap0kI/tAaFf/ RX5b3Kb8Zb2/rE/75waUuraQ043sIOiTdYjXCy9yL5s+1l7Dm2HLLXozLcTSblCb39lbwY aKgbgr6VDEPR3K15HA2SVpAQEbtVx49RWQ5743MDh5OESq6d8V+YreRECvHbAw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1601074512; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Obvuz1/Dj7IREACiXdEW9/bPBhlEoJrZlnsY+GA+QsE=; b=GqqH+xCtqvI1RVBMFcKVd4BciFBBInhDnD4zDgQ9tTa5NKS4jdtef+X2Hn+2KsL2XWdRFm VP8vIAmfY9qgW5CA== To: Adam Borowski , Greg KH Cc: Prasad Sodagudi , rostedt@goodmis.org, pmladek@suse.com, sergey.senozhatsky@gmail.com, linux-kernel@vger.kernel.org, tkjos@google.com, Mohammed Khajapasha Subject: Re: [PATCH 2/2] printk: Make the console flush configurable in hotplug path In-Reply-To: <20200925141657.GA6325@angband.pl> References: <1600906112-126722-1-git-send-email-psodagud@codeaurora.org> <1600906112-126722-2-git-send-email-psodagud@codeaurora.org> <20200924063352.GB592892@kroah.com> <87wo0j6nos.fsf@nanos.tec.linutronix.de> <20200925092754.GA2508526@kroah.com> <20200925141657.GA6325@angband.pl> Date: Sat, 26 Sep 2020 00:55:12 +0200 Message-ID: <871ripv54f.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 25 2020 at 16:16, Adam Borowski wrote: > On Fri, Sep 25, 2020 at 11:27:54AM +0200, Greg KH wrote: >> On Thu, Sep 24, 2020 at 08:21:07PM +0200, Thomas Gleixner wrote: >> > On Thu, Sep 24 2020 at 08:33, Greg KH wrote: >> > > On Wed, Sep 23, 2020 at 05:08:32PM -0700, Prasad Sodagudi wrote: >> > >> +config CONSOLE_FLUSH_ON_HOTPLUG >> > >> + bool "Enable console flush configurable in hot plug code path" > >> > CPU hotplug is not meant to be a high speed operation and if people >> > think they need it to be fast then its pretty much guaranteed that they >> > want it for the completely wrong reasons. >>=20 >> Odds are, it's the big/little systems that are trying to use cpu hotplug >> for this type of thing :( > > Just a bit of info: > My MT6797X (10 core: 4=C3=97A53 + 4=C3=97A53 + 2=C3=97A72), flickers its = cores this way: > the right-hand piece is CPUs, one character per core: bars show utilizati= on, > "o" stands for offline; every line is 0.1 second interval. > > topline -i 0.1 > mmcblk(=E2=A0=80) (oooo=E2=96=84=E2=96=86oo=E2=96=85o) > mmcblk(=E2=A0=80) (oooo=E2=96=85=E2=96=84oooo) ... > So it's on the order of a few ons/offs per second. > > The offline CPUs are "present" and "offline"; not sure if this means hotp= lug > or not (I'd expect dropping from "present" to "possible", but I don't know > these parts). Yes, they are (ab)using CPU hotplug instead of utilizing the fine grained hotplug state control and fix up the few odds and ends which keeps the CPU from staying in deep idle forever. Tinkering is way simpler than proper engineering. Thanks, tglx