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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham 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 28B0CC10F13 for ; Tue, 16 Apr 2019 17:49:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F012A2087C for ; Tue, 16 Apr 2019 17:49:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730246AbfDPRtM (ORCPT ); Tue, 16 Apr 2019 13:49:12 -0400 Received: from mga06.intel.com ([134.134.136.31]:25055 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728809AbfDPRtD (ORCPT ); Tue, 16 Apr 2019 13:49:03 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 16 Apr 2019 10:49:01 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,358,1549958400"; d="scan'208";a="224069830" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.181]) by orsmga001.jf.intel.com with ESMTP; 16 Apr 2019 10:49:01 -0700 From: Sean Christopherson To: Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= Cc: kvm@vger.kernel.org, Liran Alon , Wanpeng Li Subject: [PATCH v2 2/7] KVM: lapic: Convert guest TSC to host time domain when delaying Date: Tue, 16 Apr 2019 10:48:52 -0700 Message-Id: <20190416174857.506-3-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190416174857.506-1-sean.j.christopherson@intel.com> References: <20190416174857.506-1-sean.j.christopherson@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org To minimize the latency of timer interrupts as observed by the guest, KVM adjusts the values it programs into the host timers to account for the host's overhead of programming and handling the timer event. In the event that the adjustments are too aggressive, i.e. the timer fires earlier than the guest expects, KVM busy waits immediately prior to entering the guest. Currently, KVM manually converts the delay from nanoseconds to clock cycles. But, the conversion is done in the guest's time domain, while the delay occurs in the host's time domain, i.e. the delay may not be accurate and could wait too little or too long. Convert the delay from guest clock cycles to host nanoseconds and use ndelay() instead of __delay() to provide more accurate timing. This also avoids the need to convert lapic_timer_advance_ns, which is used to cap the delay, to guest clock cycles. Cc: Liran Alon Cc: Wanpeng Li Signed-off-by: Sean Christopherson --- arch/x86/kvm/lapic.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 92446cba9b24..5891c0badfa6 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1502,10 +1502,12 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu) guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc()); trace_kvm_wait_lapic_expire(vcpu->vcpu_id, guest_tsc - tsc_deadline); - /* __delay is delay_tsc whenever the hardware has TSC, thus always. */ - if (guest_tsc < tsc_deadline) - __delay(min(tsc_deadline - guest_tsc, - nsec_to_cycles(vcpu, lapic_timer_advance_ns))); + /* ndelay uses delay_tsc whenever the hardware has TSC, thus always. */ + if (guest_tsc < tsc_deadline) { + ns = (tsc_deadline - guest_tsc) * 1000000ULL; + do_div(ns, vcpu->arch.virtual_tsc_khz); + ndelay(min_t(u32, ns, lapic_timer_advance_ns)); + } if (!lapic_timer_advance_adjust_done) { /* too early */ -- 2.21.0