From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757514Ab3EHRDM (ORCPT ); Wed, 8 May 2013 13:03:12 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:48814 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757089Ab3EHRDK (ORCPT ); Wed, 8 May 2013 13:03:10 -0400 X-IronPort-AV: E=Sophos;i="4.87,636,1363132800"; d="scan'208";a="22930359" Date: Wed, 8 May 2013 18:03:07 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Marc Zyngier CC: Stefano Stabellini , "xen-devel@lists.xensource.com" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "konrad.wilk@oracle.com" , Will Deacon Subject: Re: [PATCH v3 4/4] xen/arm: account for stolen ticks In-Reply-To: <518A7836.4030705@arm.com> Message-ID: References: <1368027714-14506-4-git-send-email-stefano.stabellini@eu.citrix.com> <518A7836.4030705@arm.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 8 May 2013, Marc Zyngier wrote: > Hi Stefano, > > On 08/05/13 16:41, Stefano Stabellini wrote: > > Register the runstate_memory_area with the hypervisor. > > Use pv_time_ops.steal_clock to account for stolen ticks. > > > > Signed-off-by: Stefano Stabellini > > > > Changes in v3: > > - use BUG_ON and smp_processor_id. > > --- > > arch/arm/xen/enlighten.c | 22 ++++++++++++++++++++++ > > 1 files changed, 22 insertions(+), 0 deletions(-) > > > > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c > > index 13609e0..dfa7738 100644 > > --- a/arch/arm/xen/enlighten.c > > +++ b/arch/arm/xen/enlighten.c > > @@ -14,7 +14,10 @@ > > #include > > #include > > #include > > +#include > > #include > > +#include > > +#include > > #include > > #include > > #include > > @@ -152,6 +155,19 @@ int xen_unmap_domain_mfn_range(struct vm_area_struct *vma, > > } > > EXPORT_SYMBOL_GPL(xen_unmap_domain_mfn_range); > > > > +unsigned long long xen_stolen_accounting(int cpu) > > +{ > > + struct vcpu_runstate_info state; > > + > > + BUG_ON(cpu != smp_processor_id()); > > + > > + xen_get_runstate_snapshot(&state); > > + > > + WARN_ON(state.state != RUNSTATE_running); > > + > > + return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline]; > > +} > > + > > static void __init xen_percpu_init(void *unused) > > { > > struct vcpu_register_vcpu_info info; > > @@ -169,6 +185,8 @@ static void __init xen_percpu_init(void *unused) > > BUG_ON(err); > > per_cpu(xen_vcpu, cpu) = vcpup; > > > > + xen_setup_runstate_info(cpu); > > + > > enable_percpu_irq(xen_events_irq, 0); > > } > > > > @@ -300,6 +318,10 @@ static int __init xen_init_events(void) > > > > on_each_cpu(xen_percpu_init, NULL, 0); > > > > + pv_time_ops.steal_clock = xen_stolen_accounting; > > What guarantee do we have that this is done before the rest of the > kernel calls paravirt_steal_clock()? That's not a problem: paravirt_steal_clock is not called unless paravirt_steal_enabled or paravirt_steal_rq_enabled are set. Also steal_clock is always increasing so loosing the first few updates is not an issue. > What if we have Xen support enabled but don't run as a Xen guest? That's fine as long as the Xen runstate_memory_area interface is available. Usually I am a great fun of feature flags, so that every feature can be dynamically enabled or disabled and an hypervisor interface can be only partially implemented. However the runstate_memory_area is very old and I would consider it one of the core interfaces that need to be available in order to claim "Xen compatibility". > > + static_key_slow_inc(¶virt_steal_enabled); > > + static_key_slow_inc(¶virt_steal_rq_enabled); > > + > > return 0; > > } > > postcore_initcall(xen_init_events); > >