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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71F46C433EF for ; Sat, 9 Oct 2021 09:09:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 55A5060F12 for ; Sat, 9 Oct 2021 09:09:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244424AbhJIJLt (ORCPT ); Sat, 9 Oct 2021 05:11:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44656 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244346AbhJIJLp (ORCPT ); Sat, 9 Oct 2021 05:11:45 -0400 Received: from mail-pj1-x1032.google.com (mail-pj1-x1032.google.com [IPv6:2607:f8b0:4864:20::1032]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3EBE5C061570; Sat, 9 Oct 2021 02:09:49 -0700 (PDT) Received: by mail-pj1-x1032.google.com with SMTP id pf6-20020a17090b1d8600b0019fa884ab85so11009374pjb.5; Sat, 09 Oct 2021 02:09:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=5PJU+XU0vlN8es5a+TrRvmtFB7fFaJwsggeevnxxFGI=; b=QPbUET5GeEqznIKylk2KRY06RBqPOq7UCQEdiK3Sxrtyr82B2BrmGZASKYfWJfulGk jcLi/LwTgZUYVuz3aGLZjkXqvQQY2QesvS+334iuzDPRgOFyRzhKBZBM4vu34BMCV5ru h2mxSPvWLSENDLqaODvFjY69+798kY/WF0i3PJZHIzBAAk++SjBfpCMFBOaoBD+YZVSt 02U9kFDvEmbnYeWklbuy8CdKDMnn9k4byH4tw7lPoFbSILpcAlXEHWB6iRoXx9L0PUzB Oc5XEbM7qJK5Tgi5vdpKRUQ1uLPHIdhKQHgTSnVrDeQs3MgG80MzZJBnrQWxT6wvzcKY mzPg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=5PJU+XU0vlN8es5a+TrRvmtFB7fFaJwsggeevnxxFGI=; b=Fvh3OO5BO7e54hfTk2YDakGAO8HiHzvep0AXIYuOxCMs4aFZUOsQ9v3T0M1yi+mcKj WKhlPneSBbYy5Ab4Z1WuIUqKhNxNRj1slLYXP//goPN+hrTTNixlFNtVP3YFgvT65Lgv iY48snrpE0tHexpORltAnDmEBBKnODf6LF1ucqydlqRZNu+62Qvi2uHbvAwqyRLbUKrN qhFX9iciQQOghL9JRfXK2kYdtB9ebfDKtpBQqeAkZaT6sQdRJPq7kyCDge2+zRIFvZmN DyxSpDwBes5fFctcBGdpkK8Pm7efzYfIz84H333S7X6WB8s5hEetepJvsn89qFqXFHck O+PQ== X-Gm-Message-State: AOAM531DT+GdhlNKMhrdZs+N8RDrbmXST3oMyii2CnHTtuJISiO92LeH KrRX8jC7Zk1kzOcAAM2AjAHxEjstUkz1ag== X-Google-Smtp-Source: ABdhPJwQcthW8ZkvjiBpCHPmuvllL38jBJtdQzwcAhzvKHHO8zwhhD9YykNmHIH1l/hT2ICDNe5HEA== X-Received: by 2002:a17:90a:181:: with SMTP id 1mr17121215pjc.214.1633770588627; Sat, 09 Oct 2021 02:09:48 -0700 (PDT) Received: from localhost.localdomain ([203.205.141.112]) by smtp.googlemail.com with ESMTPSA id u2sm13607217pji.30.2021.10.09.02.09.46 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sat, 09 Oct 2021 02:09:48 -0700 (PDT) From: Wanpeng Li X-Google-Original-From: Wanpeng Li To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel Subject: [PATCH v2 3/3] KVM: vCPU kick tax cut for running vCPU Date: Sat, 9 Oct 2021 02:08:52 -0700 Message-Id: <1633770532-23664-3-git-send-email-wanpengli@tencent.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1633770532-23664-1-git-send-email-wanpengli@tencent.com> References: <1633770532-23664-1-git-send-email-wanpengli@tencent.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wanpeng Li Sometimes a vCPU kick is following a pending request, even if @vcpu is the running vCPU. It suffers from both rcuwait_wake_up() which has rcu/memory barrier operations and cmpxchg(). Let's check vcpu->wait before rcu_wait_wake_up() and whether @vcpu is the running vCPU before cmpxchg() to tax cut this overhead. We evaluate the kvm-unit-test/vmexit.flat on an Intel ICX box, most of the scores can improve ~600 cpu cycles especially when APICv is disabled. tscdeadline_immed tscdeadline self_ipi_sti_nop .............. x2apic_self_ipi_tpr_sti_hlt Suggested-by: Sean Christopherson Signed-off-by: Wanpeng Li --- v1 -> v2: * move checking running vCPU logic to kvm_vcpu_kick * check rcuwait_active(&vcpu->wait) etc virt/kvm/kvm_main.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7851f3a1b5f7..18209d7b3711 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3314,8 +3314,15 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu) { int me, cpu; - if (kvm_vcpu_wake_up(vcpu)) - return; + me = get_cpu(); + + if (rcuwait_active(&vcpu->wait) && kvm_vcpu_wake_up(vcpu)) + goto out; + + if (vcpu == __this_cpu_read(kvm_running_vcpu)) { + WARN_ON_ONCE(vcpu->mode == IN_GUEST_MODE); + goto out; + } /* * Note, the vCPU could get migrated to a different pCPU at any point @@ -3324,12 +3331,12 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu) * IPI is to force the vCPU to leave IN_GUEST_MODE, and migrating the * vCPU also requires it to leave IN_GUEST_MODE. */ - me = get_cpu(); if (kvm_arch_vcpu_should_kick(vcpu)) { cpu = READ_ONCE(vcpu->cpu); if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) smp_send_reschedule(cpu); } +out: put_cpu(); } EXPORT_SYMBOL_GPL(kvm_vcpu_kick); -- 2.25.1