From patchwork Fri Aug 20 08:07:26 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Zachary Amsden X-Patchwork-Id: 120543 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 o7K8FIeF004254 for ; Fri, 20 Aug 2010 08:15:18 GMT Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751929Ab0HTIId (ORCPT ); Fri, 20 Aug 2010 04:08:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38720 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751921Ab0HTII2 (ORCPT ); Fri, 20 Aug 2010 04:08:28 -0400 Received: from int-mx01.intmail.prod.int.phx2.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o7K88O2b030126 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Fri, 20 Aug 2010 04:08:24 -0400 Received: from mysore (vpn-9-158.rdu.redhat.com [10.11.9.158]) by int-mx01.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o7K87qf6027969; Fri, 20 Aug 2010 04:08:22 -0400 From: Zachary Amsden To: kvm@vger.kernel.org Cc: Zachary Amsden , Avi Kivity , Marcelo Tosatti , Glauber Costa , Thomas Gleixner , John Stultz , linux-kernel@vger.kernel.org Subject: [KVM timekeeping 12/35] Robust TSC compensation Date: Thu, 19 Aug 2010 22:07:26 -1000 Message-Id: <1282291669-25709-13-git-send-email-zamsden@redhat.com> In-Reply-To: <1282291669-25709-1-git-send-email-zamsden@redhat.com> References: <1282291669-25709-1-git-send-email-zamsden@redhat.com> X-Scanned-By: MIMEDefang 2.67 on 10.5.11.11 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]); Fri, 20 Aug 2010 08:15:18 +0000 (UTC) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 52680f6..0f3e5fb 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -928,21 +928,27 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data) struct kvm *kvm = vcpu->kvm; u64 offset, ns, elapsed; unsigned long flags; + s64 sdiff; spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags); 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);