Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751967Ab0HTIIe (ORCPT ); Fri, 20 Aug 2010 04:08:34 -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 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> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1952 Lines: 53 Make the match of TSC find TSC writes that are close to each other instead of perfectly identical; this allows the compensator to also work in migration / suspend scenarios. Signed-off-by: Zachary Amsden --- arch/x86/kvm/x86.c | 14 ++++++++++---- 1 files changed, 10 insertions(+), 4 deletions(-) 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); -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/