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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 2C3F8C43460 for ; Tue, 18 May 2021 12:02:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0FBC760231 for ; Tue, 18 May 2021 12:02:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349037AbhERMDW (ORCPT ); Tue, 18 May 2021 08:03:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49404 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348968AbhERMCy (ORCPT ); Tue, 18 May 2021 08:02:54 -0400 Received: from mail-pf1-x42d.google.com (mail-pf1-x42d.google.com [IPv6:2607:f8b0:4864:20::42d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 158B8C061756; Tue, 18 May 2021 05:01:36 -0700 (PDT) Received: by mail-pf1-x42d.google.com with SMTP id w1so4564338pfu.0; Tue, 18 May 2021 05:01:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=+j3s61DfilBbdVnALbykcBci/7JJ6WTH2JZ9k+XRHnU=; b=JoYONhNC/crNh3EiW+c93OtVBpj0HK7UEZNWa7+op6Y46s/45mG2LQxvjZeOb20Zp6 yz/dezxs45qjMBA4KvEMn62iF1Uonlb37c0JTrddjLa4CnVK+6o5DGiSGNWCiFAoV2A2 YRaJrnBwb+UlSs+z5kc6uxUNQ+6a1IEE2BWsbVIERlQqZkjGtFcUFJ3At/gBJkdwMD3o cXUREVb2h0Z6tHaIatje+Z84bYjuGafvg/noM/WmxV+vPchX3+QasW3HzrVgHVZu1i3Z zbnu1XuziJY6RTFDsqP5CQe1x3hgEgP0di1jZRN/1LNaXAc7M61pB8x601joEt5Ws5cG LCdw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=+j3s61DfilBbdVnALbykcBci/7JJ6WTH2JZ9k+XRHnU=; b=mewptrc63s16TZcx1Ok9bNR3zvp25kcKnemG1M6TEAbta3VmBvj4PCQrOzccQixq1M oejhKeKftCAOerRHalCV9HXbbrPPsByGAI16JsFzPcRRGrlYY2AKBtym4JiGJgBrBGao mYN0YNScEv71uNk4nCc5eF7gyhlhkurcYGvIzkqU6sOlhkt1s8Be6pPlNhZ/w7FwcDNK ob42YwCwdtTZxL7vz8oWSQmGnyze8z3ki3jAIbG/y5/4cj4xBizhNj+d5OIh3MHMviG0 Z8pSYhNxcpFee6F/7lylOFNrimuEvAIMzCBQuHWIsIjzORaJ282lTH39GxtFxBa0eaHz 0v8Q== X-Gm-Message-State: AOAM533mnUVfQgeOaVtWl6uRpJBcT7L59SPjTXn2uW3nP9LBF2jeHCri J8jfGQIPD5xiLJaYtooxGadyKWHRqoQ= X-Google-Smtp-Source: ABdhPJzB4JhjqKUiQijF4pjiGVjvdSRJOxy7RYQ6tKSTMs1ehMQtVyroivlCYro1QV44ABOEAObA1w== X-Received: by 2002:a05:6a00:1509:b029:2de:6765:276b with SMTP id q9-20020a056a001509b02902de6765276bmr2508738pfu.67.1621339295407; Tue, 18 May 2021 05:01:35 -0700 (PDT) Received: from localhost.localdomain ([203.205.141.53]) by smtp.googlemail.com with ESMTPSA id l20sm12757394pjq.38.2021.05.18.05.01.32 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 18 May 2021 05:01:34 -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 v4 2/5] KVM: X86: Bail out of direct yield in case of under-committed scenarios Date: Tue, 18 May 2021 05:00:32 -0700 Message-Id: <1621339235-11131-2-git-send-email-wanpengli@tencent.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1621339235-11131-1-git-send-email-wanpengli@tencent.com> References: <1621339235-11131-1-git-send-email-wanpengli@tencent.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wanpeng Li In case of under-committed scenarios, vCPU can get scheduling easily, kvm_vcpu_yield_to add extra overhead, we can observe a lot of race between vcpu->ready is true and yield fails due to p->state is TASK_RUNNING. Let's bail out in such scenarios by checking the length of current cpu runqueue, it can be treated as a hint of under-committed instead of guarantee of accuracy. The directed_yield_successful/attempted ratio can be improved from 50+% to 80+% in the under-committed scenario. Signed-off-by: Wanpeng Li --- v2 -> v3: * update patch description v1 -> v2: * move the check after attempted counting * update patch description arch/x86/kvm/x86.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9b6bca616929..dfb7c320581f 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8360,6 +8360,9 @@ static void kvm_sched_yield(struct kvm_vcpu *vcpu, unsigned long dest_id) vcpu->stat.directed_yield_attempted++; + if (single_task_running()) + goto no_yield; + rcu_read_lock(); map = rcu_dereference(vcpu->kvm->arch.apic_map); -- 2.25.1