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 AC363C6FA82 for ; Fri, 23 Sep 2022 07:05:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230036AbiIWHF5 (ORCPT ); Fri, 23 Sep 2022 03:05:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43300 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230098AbiIWHFx (ORCPT ); Fri, 23 Sep 2022 03:05:53 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D6FD011F111 for ; Fri, 23 Sep 2022 00:05:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=fQbe8Qt2OMSbhVmXxMJpTQEENy8N/rtwxDABlBmr4k8=; b=X36Z/ZtDiwDwkEjDB+qxcAOJoT eiHFgnPY3GMMUQCiNiVKslJaWjzlZic9Yhtq9vqdwi6zCnhta16P+1TRke+E85V6cMDwLB4WT8jge 0Np3N/gxq7eeLtzIQ3u6ylXccRBAwGYDJDxG7kkUB6QzpkCSYKhWN9d+YAbF/xf0Lois+QoJ/c919 RVv5KLjPfvTvjuGyKr6Jg5Ny188keAKDhHkkUva1odzSIp1HxDpMpNOlmxGBReS2NiP97d4vCkpn6 KiXqzp+dqFjB0NLyC7ZeLmwOJ41ktT699EzB6rORGycet+/Lmc6sdKcs2JBfcIEF95IYwN8koWc9A 5VMCUGcw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1obckY-00F9ug-VC; Fri, 23 Sep 2022 07:05:27 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 497B7300074; Fri, 23 Sep 2022 09:05:26 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2B8ED2BC39437; Fri, 23 Sep 2022 09:05:26 +0200 (CEST) Date: Fri, 23 Sep 2022 09:05:26 +0200 From: Peter Zijlstra To: "Srivatsa S. Bhat" Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Alexey Makhalov , Juergen Gross , x86@kernel.org, VMware PV-Drivers Reviewers , ganb@vmware.com, sturlapati@vmware.com, bordoloih@vmware.com, ankitja@vmware.com, keerthanak@vmware.com, namit@vmware.com, srivatsab@vmware.com Subject: Re: [PATCH] smp/hotplug, x86/vmware: Put offline vCPUs in halt instead of mwait Message-ID: References: <165843627080.142207.12667479241667142176.stgit@csail.mit.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <165843627080.142207.12667479241667142176.stgit@csail.mit.edu> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 21, 2022 at 01:44:33PM -0700, Srivatsa S. Bhat wrote: > From: Srivatsa S. Bhat (VMware) > > VMware ESXi allows enabling a passthru mwait CPU-idle state in the > guest using the following VMX option: > > monitor_control.mwait_in_guest = "TRUE" > > This lets a vCPU in mwait to remain in guest context (instead of > yielding to the hypervisor via a VMEXIT), which helps speed up > wakeups from idle. > > However, this runs into problems with CPU hotplug, because the Linux > CPU offline path prefers to put the vCPU-to-be-offlined in mwait > state, whenever mwait is available. As a result, since a vCPU in mwait > remains in guest context and does not yield to the hypervisor, an > offline vCPU *appears* to be 100% busy as viewed from ESXi, which > prevents the hypervisor from running other vCPUs or workloads on the > corresponding pCPU (particularly when vCPU - pCPU mappings are > statically defined by the user). I would hope vCPU pinning is a mandatory thing when MWAIT passthrough it set? > [ Note that such a vCPU is not > actually busy spinning though; it remains in mwait idle state in the > guest ]. > > Fix this by overriding the CPU offline play_dead() callback for VMware > hypervisor, by putting the CPU in halt state (which actually yields to > the hypervisor), even if mwait support is available. > > Signed-off-by: Srivatsa S. Bhat (VMware) > --- > +static void vmware_play_dead(void) > +{ > + play_dead_common(); > + tboot_shutdown(TB_SHUTDOWN_WFS); > + > + /* > + * Put the vCPU going offline in halt instead of mwait (even > + * if mwait support is available), to make sure that the > + * offline vCPU yields to the hypervisor (which may not happen > + * with mwait, for example, if the guest's VMX is configured > + * to retain the vCPU in guest context upon mwait). > + */ > + hlt_play_dead(); > +} > #endif > > static __init int activate_jump_labels(void) > @@ -349,6 +365,7 @@ static void __init vmware_paravirt_ops_setup(void) > #ifdef CONFIG_SMP > smp_ops.smp_prepare_boot_cpu = > vmware_smp_prepare_boot_cpu; > + smp_ops.play_dead = vmware_play_dead; > if (cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, > "x86/vmware:online", > vmware_cpu_online, No real objection here; but would not something like the below fix the problem more generally? I'm thinking MWAIT passthrough for *any* hypervisor doesn't want play_dead to use it. diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index f24227bc3220..166cb3aaca8a 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1759,6 +1759,8 @@ static inline void mwait_play_dead(void) return; if (!this_cpu_has(X86_FEATURE_CLFLUSH)) return; + if (this_cpu_has(X86_FEATURE_HYPERVISOR)) + return; if (__this_cpu_read(cpu_info.cpuid_level) < CPUID_MWAIT_LEAF) return;