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 E2293C433EF for ; Fri, 20 May 2022 15:38:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350903AbiETPia (ORCPT ); Fri, 20 May 2022 11:38:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58592 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344615AbiETPi2 (ORCPT ); Fri, 20 May 2022 11:38:28 -0400 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E2E729D05C for ; Fri, 20 May 2022 08:38:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1653061107; x=1684597107; h=message-id:subject:from:to:cc:date:in-reply-to: references:mime-version:content-transfer-encoding; bh=FTcYXObNA72+JfxB9UBcj9N5vY/n/OK6No5jETfhSeQ=; b=XigNgZyMyKxRuG0zyupy9og5KeSHEmflANghRU84Hm8GpNC8w6CIhdWc COSCFwaSaKarnUEIu10wcGgsEuiPAj9flf8WB+y4GwuIxyZq7fyT8AB5p ipz/u2CAxhhM+UXUiH0QFcYKI/AsM8llWCaNWLn79mwHZOXClj5zDL4qR wEwCdaO2vS9mLu+ECNLnUDPvfLJ3kFco3OP/j3cCFZIjNv/Ok6705yws9 2pCW2yLRYvWPYh0xt1PB9hnhGuqrd/JZshd3k0S/AoS0g7p7vd0L/2ihV TevAy+LzSYYPhk8b18W9drGDXspPS9tjqmQGvQVRnboI32nWfyPCdryjf g==; X-IronPort-AV: E=McAfee;i="6400,9594,10353"; a="359042209" X-IronPort-AV: E=Sophos;i="5.91,239,1647327600"; d="scan'208";a="359042209" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 May 2022 08:38:26 -0700 X-IronPort-AV: E=Sophos;i="5.91,239,1647327600"; d="scan'208";a="599278128" Received: from yyan7-mobl1.ccr.corp.intel.com ([10.255.31.53]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 May 2022 08:38:19 -0700 Message-ID: Subject: Re: [PATCH v3 1/3] x86: Use HLT in default_idle when idle=nomwait cmdline arg is passed 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: Fri, 20 May 2022 23:38:17 +0800 In-Reply-To: <1b24cadcf1d86a91352baa13905218015b9d4fed.1652176835.git-series.wyes.karny@amd.com> References: <1b24cadcf1d86a91352baa13905218015b9d4fed.1652176835.git-series.wyes.karny@amd.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 Hi, Wyes, On Tue, 2022-05-10 at 15:48 +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. I think we also need to update the comment in idle_setup() as well. } 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 * states. In such case it won't touch the variable * of boot_option_idle_override. */ boot_op tion_idle_override = IDLE_NOMWAIT; } else thanks, rui > > Signed-off-by: Wyes Karny > --- > Changes in v3: > - Update documentation around idle=mwait > > Documentation/admin-guide/pm/cpuidle.rst | 15 +++++++++------ > arch/x86/kernel/process.c | 4 ++++ > 2 files changed, 13 insertions(+), 6 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..49b915d1b7b4 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; >