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 23307C433B4 for ; Tue, 18 May 2021 12:02:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 08B2F610CD for ; Tue, 18 May 2021 12:02:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349078AbhERMDa (ORCPT ); Tue, 18 May 2021 08:03:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49454 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348997AbhERMDC (ORCPT ); Tue, 18 May 2021 08:03:02 -0400 Received: from mail-pf1-x435.google.com (mail-pf1-x435.google.com [IPv6:2607:f8b0:4864:20::435]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5E400C061761; Tue, 18 May 2021 05:01:44 -0700 (PDT) Received: by mail-pf1-x435.google.com with SMTP id b13so3477992pfv.4; Tue, 18 May 2021 05:01:44 -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=soOUzbLJHd79dLzXUneFH08UM8yTlNutja4acLt0+qU=; b=hIdVLuZbbk0swz4hpVBO5hP1ydSkuNP4SwlXYVJ4f2xrIqZy7KGaH9grl6v6LlNJLY bDirjnkwMnbG96k6JaFACCjjPV3taK7feKB/DCqVY8eq4jpnFPXi3V5pOs3ZevSSzdaj qXSii3s1GknciQzSYzAYHIsP951Uzqo6egApt9F8IVg0MfgNjio+FwycWiJSDO7nCHOv 08n40f/UU7WaAZY5IPClwkxtiRyiFD4z2Mh3id4MXy4nuKcyMZIqm0jl1uMxa4uYv0p1 ljY1NyOs1CbzGigFkjqB2GHMVfqaiPTF8oB7984LCCzOTS/8795Ug1xMRoddTNoyU2BW K+Kg== 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=soOUzbLJHd79dLzXUneFH08UM8yTlNutja4acLt0+qU=; b=ncurSObIRNDrVewa6ONUlxk1LzWx1mCvkmL6Opcn9ytT/LM3eUi7WJCW3/lnBlnHz5 uMf5BRmw/a+FjG45hFa4gb06RoabrO1yM/FLGHEbafSyV+YkUN0LVEVxS4J3nW4xxdPc Opq3lCK+Lpsf9imhArM6mSEUAlzr/LgWhMu/7h3XJmQ1Fze+bGnqkaCHaY5diD2usIHA l7ojQ120r+Y5jUMN029Rn4PmPAsIrktN/SA5lOKQ2NLBuC0lMM+WABKFL8oUNm/P3E1I z0KYAZPjhvcUPghWhidaVhJQobSZvN/GXbpZWKvTOrKi0H1GBV7pEzzr5WB8uVDRWBFH YQMQ== X-Gm-Message-State: AOAM533lD7Rec7V1kmH4RXBlvIPz5AYZWGkMufDTgfiXRdusPkLUOxIW uNlHJwburaF8y3sY3oBLabvkjfGc0tw= X-Google-Smtp-Source: ABdhPJztev0nvWB7p2r+uTPVQkH9uSr4620Rogko2ex6afamBnUY4Y+8h39mp42uX4FtDw+3fhQjsQ== X-Received: by 2002:a63:d744:: with SMTP id w4mr4791316pgi.76.1621339303764; Tue, 18 May 2021 05:01:43 -0700 (PDT) Received: from localhost.localdomain ([203.205.141.53]) by smtp.googlemail.com with ESMTPSA id l20sm12757394pjq.38.2021.05.18.05.01.41 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 18 May 2021 05:01:43 -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 5/5] KVM: LAPIC: Narrow the timer latency between wait_lapic_expire and world switch Date: Tue, 18 May 2021 05:00:35 -0700 Message-Id: <1621339235-11131-5-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 Let's treat lapic_timer_advance_ns automatic tuning logic as hypervisor overhead, move it before wait_lapic_expire instead of between wait_lapic_expire and the world switch, the wait duration should be calculated by the up-to-date guest_tsc after the overhead of automatic tuning logic. This patch reduces ~30+ cycles for kvm-unit-tests/tscdeadline-latency when testing busy waits. Signed-off-by: Wanpeng Li --- v3 -> v4: * consider automatic tuning is disabled and timer did not arrive early * add a code comment arch/x86/kvm/lapic.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index c0ebef560bd1..5d91f2367c31 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1598,11 +1598,19 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu) guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc()); apic->lapic_timer.advance_expire_delta = guest_tsc - tsc_deadline; + if (lapic_timer_advance_dynamic) { + adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta); + /* + * If the timer fired early, reread the TSC to account for the + * overhead of the above adjustment to avoid waiting longer + * than is necessary. + */ + if (guest_tsc < tsc_deadline) + guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc()); + } + if (guest_tsc < tsc_deadline) __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc); - - if (lapic_timer_advance_dynamic) - adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta); } void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu) -- 2.25.1