From patchwork Tue Jul 13 02:25:29 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Zachary Amsden X-Patchwork-Id: 111640 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by demeter.kernel.org (8.14.4/8.14.3) with ESMTP id o6D2Sw65015430 for ; Tue, 13 Jul 2010 02:28:58 GMT Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752414Ab0GMC17 (ORCPT ); Mon, 12 Jul 2010 22:27:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:5408 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756684Ab0GMC0D (ORCPT ); Mon, 12 Jul 2010 22:26:03 -0400 Received: from int-mx05.intmail.prod.int.phx2.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.18]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o6D2Q3kO004795 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Mon, 12 Jul 2010 22:26:03 -0400 Received: from mysore (vpn-10-168.rdu.redhat.com [10.11.10.168]) by int-mx05.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o6D2Pfie026035; Mon, 12 Jul 2010 22:26:01 -0400 From: Zachary Amsden To: KVM , Avi Kivity , Marcelo Tosatti , Glauber Costa Cc: Linux-kernel , Zachary Amsden , Avi Kivity , Marcelo Tosatti , Glauber Costa Subject: [PATCH 09/18] Robust TSC compensation Date: Mon, 12 Jul 2010 16:25:29 -1000 Message-Id: <1278987938-23873-10-git-send-email-zamsden@redhat.com> In-Reply-To: <1278987938-23873-1-git-send-email-zamsden@redhat.com> References: <1278987938-23873-1-git-send-email-zamsden@redhat.com> X-Scanned-By: MIMEDefang 2.67 on 10.5.11.18 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Greylist: IP, sender and recipient auto-whitelisted, not delayed by milter-greylist-4.2.3 (demeter.kernel.org [140.211.167.41]); Tue, 13 Jul 2010 02:28:58 +0000 (UTC) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 79c4608..51d3f3e 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -926,21 +926,27 @@ void guest_write_tsc(struct kvm_vcpu *vcpu, u64 data) struct kvm *kvm = vcpu->kvm; u64 offset, ns, elapsed; struct timespec ts; + s64 sdiff; spin_lock(&kvm->arch.tsc_write_lock); offset = data - native_read_tsc(); ns = get_kernel_ns(); elapsed = ns - kvm->arch.last_tsc_nsec; + sdiff = data - kvm->arch.last_tsc_write; + if (sdiff < 0) + sdiff = -sdiff; /* - * Special case: identical write to TSC within 5 seconds of + * Special case: close write to TSC within 5 seconds of * another CPU is interpreted as an attempt to synchronize - * (the 5 seconds is to accomodate host load / swapping). + * The 5 seconds is to accomodate host load / swapping as + * well as any reset of TSC during the boot process. * * In that case, for a reliable TSC, we can match TSC offsets, - * or make a best guest using kernel_ns value. + * or make a best guest using elapsed value. */ - if (data == kvm->arch.last_tsc_write && elapsed < 5ULL * NSEC_PER_SEC) { + if (sdiff < nsec_to_cycles(5ULL * NSEC_PER_SEC) && + elapsed < 5ULL * NSEC_PER_SEC) { if (!check_tsc_unstable()) { offset = kvm->arch.last_tsc_offset; pr_debug("kvm: matched tsc offset for %llu\n", data);