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=-5.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 344BEC4363D for ; Fri, 25 Sep 2020 09:27:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D8B682076D for ; Fri, 25 Sep 2020 09:27:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601026061; bh=uKVo2+xjnMrqEkSD18awjmWEkwFPN07/VkgovTxNUx4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=IRDb/TTO1yaBQT5yQu7uQF8tdA1fKBS9Hrp3zapi2OxKsANOuIQn20Kn+ovPLQWZc l76vnFrCtamHuGCgv7e32s4t7eRnZqq4hvVmASqNjF5JAgsTlwXs1agofkZ2sWiar3 WUf3zfSJJlJ0dESrXXtt1ktzTH1eg3L4BhoOTD70= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727837AbgIYJ1k (ORCPT ); Fri, 25 Sep 2020 05:27:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:56206 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727132AbgIYJ1k (ORCPT ); Fri, 25 Sep 2020 05:27:40 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 37C0F20738; Fri, 25 Sep 2020 09:27:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601026059; bh=uKVo2+xjnMrqEkSD18awjmWEkwFPN07/VkgovTxNUx4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=d3KU8LhZrK1BhkLPLTgRXfndVrB2RE7Cq6t4TquevajpNIf8iImULIwz2OGmvhydW P7y0Qsay7e42+bMrWjPOM0a8AfdIssaLh9spTFjvCviqZV7DIBLWC/hZuppQ5ds1ag vC77lvGkPrZ9NIEnHi9YNWSUmVcHIwYapI5jIuK4= Date: Fri, 25 Sep 2020 11:27:54 +0200 From: Greg KH To: Thomas Gleixner 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 Message-ID: <20200925092754.GA2508526@kroah.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87wo0j6nos.fsf@nanos.tec.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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" > >> + depends on HOTPLUG_CPU > >> + def_bool n > > > > n is the default, no need to list it. > > > >> + help > >> + In cpu hot plug path console lock acquire and release causes the > >> + console to flush. If console lock is not free hot plug latency > >> + increases. So make console flush configurable in hot plug path > >> + and default disabled to help in cpu hot plug latencies. > > > > Why would you not want this option? > > > > Why isn't this just a bugfix? > > Because it's the normal behaviour of console lock and there are > gazillion other ways to delay stuff in the hotplug 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. Odds are, it's the big/little systems that are trying to use cpu hotplug for this type of thing :( > This #ifdef tinkering is just digusting especially as it just tackles an > obvious way how to delay timer migration, but does not address the > underlying root cause. Agreed, thanks for putting it better than I did. greg k-h