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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 E6FEACA9EBC for ; Thu, 24 Oct 2019 01:22:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C7DDA2086D for ; Thu, 24 Oct 2019 01:22:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392346AbfJXBWq (ORCPT ); Wed, 23 Oct 2019 21:22:46 -0400 Received: from mga09.intel.com ([134.134.136.24]:46317 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726925AbfJXBWq (ORCPT ); Wed, 23 Oct 2019 21:22:46 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 23 Oct 2019 18:22:45 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.68,222,1569308400"; d="scan'208";a="228325784" Received: from fyin-dev.sh.intel.com (HELO [10.239.143.122]) ([10.239.143.122]) by fmsmga002.fm.intel.com with ESMTP; 23 Oct 2019 18:22:44 -0700 Subject: Re: [PATCH v3] ACPI/processor_idle: Remove dummy wait if kernel is in guest mode To: "Rafael J. Wysocki" , David Laight Cc: "linux-kernel@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "rjw@rjwysocki.net" , "lenb@kernel.org" References: <20191023074945.17016-1-fengwei.yin@intel.com> <30ee0a348f624698801691f65eeecd87@AcuMS.aculab.com> From: Yin Fengwei Message-ID: <07760c4a-b3f0-83a3-ed1b-6df45f8deb35@intel.com> Date: Thu, 24 Oct 2019 09:22:42 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/10/23 下午5:03, Rafael J. Wysocki wrote: > On Wed, Oct 23, 2019 at 10:45 AM David Laight wrote: >> >> From: Yin Fengwei >>> Sent: 23 October 2019 08:50 >> >> >>> In function acpi_idle_do_entry(), an ioport access is used for dummy >>> wait to guarantee hardware behavior. But it could trigger unnecessary >>> vmexit if kernel is running as guest in virtualization environtment. >>> >>> If it's in virtualization environment, the deeper C state enter >>> operation (inb()) will trap to hyervisor. It's not needed to do >>> dummy wait after the inb() call. So we remove the dummy io port >>> access to avoid unnecessary VMexit. >>> >>> We keep dummy io port access to maintain timing for native environment. >>> >>> Signed-off-by: Yin Fengwei >>> --- >>> ChangeLog: >>> v2 -> v3: >>> - Remove dummy io port access totally for virtualization env. >>> >>> v1 -> v2: >>> - Use ndelay instead of dead loop for dummy delay. >>> >>> drivers/acpi/processor_idle.c | 36 ++++++++++++++++++++++++++++++++--- >>> 1 file changed, 33 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c >>> index ed56c6d20b08..0c4a97dd6917 100644 >>> --- a/drivers/acpi/processor_idle.c >>> +++ b/drivers/acpi/processor_idle.c >>> @@ -58,6 +58,17 @@ struct cpuidle_driver acpi_idle_driver = { >>> static >>> DEFINE_PER_CPU(struct acpi_processor_cx * [CPUIDLE_STATE_MAX], acpi_cstate); >>> >>> +static void (*dummy_wait)(u64 address); >>> + >>> +static void default_dummy_wait(u64 address) >>> +{ >>> + inl(address); >>> +} >>> + >>> +static void default_noop_wait(u64 address) >>> +{ >>> +} >>> + >> >> Overengineered... >> Just add: >> >> static void wait_for_freeze(void) >> { >> #ifdef CONFIG_X86 >> /* No delay is needed if we are a guest */ >> if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) >> return; >> #endif >> >> /* Dummy wait op - must do something useless after P_LVL2 read >> because chipsets cannot guarantee that STPCLK# signal >> gets asserted in time to freeze execution properly. */ >> inl(acpi_gbl_FADT.xpm_timer_block.address); >> } >> >> and use it to replace the inl(). > > I was about to make a similar comment. OK. Will send v4 soon. Regards Yin, Fengwei >