Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756525Ab0GMCIx (ORCPT ); Mon, 12 Jul 2010 22:08:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15521 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756398Ab0GMCIu (ORCPT ); Mon, 12 Jul 2010 22:08:50 -0400 From: Zachary Amsden To: KVM , Avi Kivity , Marcelo Tosatti , Glauber Costa Cc: Linux-kernel , Zachary Amsden Subject: [PATCH 03/18] TSC reset compensation Date: Mon, 12 Jul 2010 16:07:57 -1000 Message-Id: <1278986892-11733-4-git-send-email-zamsden@redhat.com> In-Reply-To: <1278986892-11733-1-git-send-email-zamsden@redhat.com> References: <1278986892-11733-1-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: 2661 Lines: 78 Attempt to synchronize TSCs which are reset to the same value. In the case of a reliable hardware TSC, we can just re-use the same offset, but on non-reliable hardware, we can get closer by adjusting the offset to match the elapsed time. Signed-off-by: Zachary Amsden --- arch/x86/include/asm/kvm_host.h | 3 +++ arch/x86/kvm/x86.c | 31 ++++++++++++++++++++++++++++++- 2 files changed, 33 insertions(+), 1 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 3b4efe2..4b42893 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -396,6 +396,9 @@ struct kvm_arch { unsigned long irq_sources_bitmap; s64 kvmclock_offset; spinlock_t tsc_write_lock; + u64 last_tsc_nsec; + u64 last_tsc_offset; + u64 last_tsc_write; struct kvm_xen_hvm_config xen_hvm_config; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a2ee975..bb7451b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -896,10 +896,39 @@ static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz); void guest_write_tsc(struct kvm_vcpu *vcpu, u64 data) { struct kvm *kvm = vcpu->kvm; - u64 offset; + u64 offset, ns, elapsed; + struct timespec ts; spin_lock(&kvm->arch.tsc_write_lock); offset = data - native_read_tsc(); + ktime_get_ts(&ts); + monotonic_to_bootbased(&ts); + ns = timespec_to_ns(&ts); + elapsed = ns - kvm->arch.last_tsc_nsec; + + /* + * Special case: identical 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). + * + * In that case, for a reliable TSC, we can match TSC offsets, + * or make a best guest using kernel_ns value. + */ + if (data == kvm->arch.last_tsc_write && 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); + } else { + u64 tsc_delta = elapsed * __get_cpu_var(cpu_tsc_khz); + tsc_delta = tsc_delta / USEC_PER_SEC; + offset += tsc_delta; + pr_debug("kvm: adjusted tsc offset by %llu\n", tsc_delta); + } + ns = kvm->arch.last_tsc_nsec; + } + kvm->arch.last_tsc_nsec = ns; + kvm->arch.last_tsc_write = data; + kvm->arch.last_tsc_offset = offset; kvm_x86_ops->write_tsc_offset(vcpu, offset); spin_unlock(&kvm->arch.tsc_write_lock); -- 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/