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 CA82FC43334 for ; Sun, 5 Jun 2022 12:33:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245706AbiFEMdE (ORCPT ); Sun, 5 Jun 2022 08:33:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54052 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231252AbiFEMdB (ORCPT ); Sun, 5 Jun 2022 08:33:01 -0400 Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 73BB360E0 for ; Sun, 5 Jun 2022 05:33:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1654432380; x=1685968380; h=message-id:subject:from:to:cc:date:in-reply-to: references:mime-version:content-transfer-encoding; bh=IckfVGVO7Hb5OLHEwMcHe7yP/DG2W6pd5rQ6ihMI/R0=; b=CdaZFKEOo3xYQDJP53jJOdIQKGQWIKdCjqsqD46F7XqoiPRfRWapq0KD ++ieRt0l8zVNB+ebPjAswrZjGLUFRZqGzdB2Zat4ZWsaw4P+g4KPGZfhW dpN1+NNUwXuhZ/3m1xS+JU+KeFa9+G1QxINoNQzReiVfaexiACZD7Kvjw 8shF0cQ0v2gdxh5P+rhELKA7ANQNgEJ5IAUFKx1u5CVbWRZwS3VmqU42p aLrHGPcWRhE2t7rCl9NH0QuFYozbJmU1e4hK6rWTbTeEzOH4Tm6K8kac9 tTHISUiApM/PXe6HEYd1DpEiZLWH2d4v5mGL3eZfRA86BGoGn7ZrqkgvH w==; X-IronPort-AV: E=McAfee;i="6400,9594,10368"; a="258649566" X-IronPort-AV: E=Sophos;i="5.91,279,1647327600"; d="scan'208";a="258649566" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Jun 2022 05:32:59 -0700 X-IronPort-AV: E=Sophos;i="5.91,279,1647327600"; d="scan'208";a="553996454" Received: from jhuan46-mobl1.ccr.corp.intel.com ([10.255.30.107]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Jun 2022 05:32:53 -0700 Message-ID: Subject: Re: [PATCH v4 1/3] x86: Handle idle=nomwait cmdline properly for x86_idle From: Zhang Rui To: Wyes Karny , linux-kernel@vger.kernel.org Cc: Lewis.Carroll@amd.com, Mario.Limonciello@amd.com, gautham.shenoy@amd.com, Ananth.Narayan@amd.com, bharata@amd.com, len.brown@intel.com, x86@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, peterz@infradead.org, chang.seok.bae@intel.com, keescook@chromium.org, metze@samba.org, zhengqi.arch@bytedance.com, mark.rutland@arm.com, puwen@hygon.cn, rafael.j.wysocki@intel.com, andrew.cooper3@citrix.com, jing2.liu@intel.com, jmattson@google.com, pawan.kumar.gupta@linux.intel.com Date: Sun, 05 Jun 2022 20:32:51 +0800 In-Reply-To: References: <7e5a66c4d383652c89a0b5ec0f57e0a95902f810.1653324016.git-series.wyes.karny@amd.com> <9dde86ab8773ddf3f9d88a85ed9ee010cdcf50a8.camel@intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2022-06-02 at 21:11 +0530, Wyes Karny wrote: > > > > Hi Rui, > > On 5/25/2022 1:36 PM, Zhang Rui wrote: > > On Mon, 2022-05-23 at 22:25 +0530, Wyes Karny wrote: > > > When kernel is booted with idle=nomwait do not use MWAIT as the > > > default idle state. > > > > > > If the user boots the kernel with idle=nomwait, it is a clear > > > direction to not use mwait as the default idle state. > > > However, the current code does not take this into consideration > > > while selecting the default idle state on x86. > > > > > > This patch fixes it by checking for the idle=nomwait boot option > > > in > > > prefer_mwait_c1_over_halt(). > > > > > > Also update the documentation around idle=nomwait appropriately. > > > > > > Signed-off-by: Wyes Karny > > > --- > > > Changes in v4: > > > - Update documentation around idle=nomwait > > > - Rename patch subject > > > > > > Documentation/admin-guide/pm/cpuidle.rst | 15 +++++++++------ > > > arch/x86/kernel/process.c | 6 +++++- > > > 2 files changed, 14 insertions(+), 7 deletions(-) > > > > > > diff --git a/Documentation/admin-guide/pm/cpuidle.rst > > > b/Documentation/admin-guide/pm/cpuidle.rst > > > index aec2cd2aaea7..19754beb5a4e 100644 > > > --- a/Documentation/admin-guide/pm/cpuidle.rst > > > +++ b/Documentation/admin-guide/pm/cpuidle.rst > > > @@ -612,8 +612,8 @@ the ``menu`` governor to be used on the > > > systems > > > that use the ``ladder`` governor > > > by default this way, for example. > > > > > > The other kernel command line parameters controlling CPU idle > > > time > > > management > > > -described below are only relevant for the *x86* architecture and > > > some of > > > -them affect Intel processors only. > > > +described below are only relevant for the *x86* architecture and > > > references > > > +to ``intel_idle`` affect Intel processors only. > > > > > > The *x86* architecture support code recognizes three kernel > > > command > > > line > > > options related to CPU idle time management: ``idle=poll``, > > > ``idle=halt``, > > > @@ -635,10 +635,13 @@ idle, so it very well may hurt single- > > > thread > > > computations performance as well as > > > energy-efficiency. Thus using it for performance reasons may > > > not be > > > a good idea > > > at all.] > > > > > > -The ``idle=nomwait`` option disables the ``intel_idle`` driver > > > and > > > causes > > > -``acpi_idle`` to be used (as long as all of the information > > > needed > > > by it is > > > -there in the system's ACPI tables), but it is not allowed to use > > > the > > > -``MWAIT`` instruction of the CPUs to ask the hardware to enter > > > idle > > > states. > > > +The ``idle=nomwait`` option prevents the use of ``MWAIT`` > > > instruction of > > > +the CPU to enter idle states. When this option is used, the > > > ``acpi_idle`` > > > +driver will use the ``HLT`` instruction instead of ``MWAIT``. On > > > systems > > > +running Intel processors, this option disables the > > > ``intel_idle`` > > > driver > > > +and forces the use of the ``acpi_idle`` driver instead. Note > > > that in > > > either > > > +case, ``acpi_idle`` driver will function only if all the > > > information > > > needed > > > +by it is in the system's ACPI tables. > > > > > > In addition to the architecture-level kernel command line > > > options > > > affecting CPU > > > idle time management, there are parameters affecting individual > > > ``CPUIdle`` > > > diff --git a/arch/x86/kernel/process.c > > > b/arch/x86/kernel/process.c > > > index b370767f5b19..4e0178b066c5 100644 > > > --- a/arch/x86/kernel/process.c > > > +++ b/arch/x86/kernel/process.c > > > @@ -824,6 +824,10 @@ static void amd_e400_idle(void) > > > */ > > > static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 > > > *c) > > > { > > > + /* User has disallowed the use of MWAIT. Fallback to HALT */ > > > + if (boot_option_idle_override == IDLE_NOMWAIT) > > > + return 0; > > > + > > > if (c->x86_vendor != X86_VENDOR_INTEL) > > > return 0; > > > > > > @@ -932,7 +936,7 @@ static int __init idle_setup(char *str) > > > } else if (!strcmp(str, "nomwait")) { > > > /* > > > * If the boot option of "idle=nomwait" is added, > > > - * it means that mwait will be disabled for CPU C2/C3 > > > + * it means that mwait will be disabled for CPU > > > C1/C2/C3 > > > * states. In such case it won't touch the variable > > > * of boot_option_idle_override. > > > > the code didn't change boot_option_idle_override when it was > > introduced, but this has changed since commit d18960494f65 ("ACPI, > > intel_idle: Cleanup idle= internal variables") > > Could you please clarify bit more why the commit you mentioned is > related to this patch? > The comment "In such case it won't touch the variable of boot_option_idle_override." has been broken for some time, it is not related with this patch. But given that this patch "Also update the documentation around idle=nomwait appropriately", so my suggestion is to update it altogether, by deleting the last sentence. thanks, rui