From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: [PATCH v2] KVM: x86: add module parameter to disable periodic kvmclock sync Date: Tue, 12 May 2015 22:42:04 -0300 Message-ID: <20150513014203.GA8981@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Andrew Jones , Luiz Capitulino To: kvm-devel Return-path: Received: from mx1.redhat.com ([209.132.183.28]:39117 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964912AbbEMBme (ORCPT ); Tue, 12 May 2015 21:42:34 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (Postfix) with ESMTPS id B059B8EB5A for ; Wed, 13 May 2015 01:42:34 +0000 (UTC) Content-Disposition: inline Sender: kvm-owner@vger.kernel.org List-ID: The periodic kvmclock sync can be an undesired source of latencies. When running cyclictest on a guest, a latency spike is visible. With kvmclock periodic sync disabled, the spike is gone. Guests should use ntp which means the propagations of ntp corrections from the host clock are unnecessary. v2: -> Make parameter read-only (Radim) -> Return early on kvmclock_sync_fn (Andrew) Reported-and-tested-by: Luiz Capitulino Signed-off-by: Marcelo Tosatti diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 986b3f5..4c0c954 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -99,6 +99,9 @@ module_param(ignore_msrs, bool, S_IRUGO | S_IWUSR); unsigned int min_timer_period_us = 500; module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR); +static bool __read_mostly kvmclock_periodic_sync = true; +module_param(kvmclock_periodic_sync, bool, S_IRUGO); + bool kvm_has_tsc_control; EXPORT_SYMBOL_GPL(kvm_has_tsc_control); u32 kvm_max_guest_tsc_khz; @@ -1768,6 +1771,9 @@ static void kvmclock_sync_fn(struct work_struct *work) kvmclock_sync_work); struct kvm *kvm = container_of(ka, struct kvm, arch); + if (!kvmclock_periodic_sync) + return; + schedule_delayed_work(&kvm->arch.kvmclock_update_work, 0); schedule_delayed_work(&kvm->arch.kvmclock_sync_work, KVMCLOCK_SYNC_PERIOD); @@ -7109,6 +7115,9 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu) kvm_write_tsc(vcpu, &msr); vcpu_put(vcpu); + if (!kvmclock_periodic_sync) + return; + schedule_delayed_work(&kvm->arch.kvmclock_sync_work, KVMCLOCK_SYNC_PERIOD); }