linux-kernel - Re: [PATCH] KVM: trace the events of mmu

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Date:	Thu, 23 Aug 2012 10:08:20 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: trace the events of mmu_notifier

On Thu, Aug 23, 2012 at 08:30:15PM +0800, Xiao Guangrong wrote:
> On 08/23/2012 05:24 PM, Marcelo Tosatti wrote:
> > On Tue, Aug 21, 2012 at 05:51:35PM +0800, Xiao Guangrong wrote:
> >> mmu_notifier is the interface to broadcast the mm events to KVM, the
> >> tracepoints introduced in this patch can trace all these events, it is
> >> very helpful for us to notice and fix the bug caused by mm
> >>
> >> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> >> ---
> >>  include/trace/events/kvm.h |  121 ++++++++++++++++++++++++++++++++++++++++++++
> >>  virt/kvm/kvm_main.c        |   19 +++++++
> >>  2 files changed, 140 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h
> >> index 7ef9e75..a855ff9 100644
> >> --- a/include/trace/events/kvm.h
> >> +++ b/include/trace/events/kvm.h
> >> @@ -309,6 +309,127 @@ TRACE_EVENT(
> >>
> >>  #endif
> >>
> >> +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> >> +DECLARE_EVENT_CLASS(mmu_notifier_address_class,
> >> +
> >> +	TP_PROTO(struct kvm *kvm, unsigned long address),
> >> +
> >> +	TP_ARGS(kvm, address),
> >> +
> >> +	TP_STRUCT__entry(
> >> +		__field(struct kvm *, kvm)
> >> +		__field(unsigned long, address)
> >> +	),
> >> +
> >> +	TP_fast_assign(
> >> +		__entry->kvm = kvm;
> >> +		__entry->address = address;
> >> +	),
> >> +
> >> +	TP_printk("kvm %p address %lx", __entry->kvm, __entry->address)
> > 
> > 
> > Perhaps the pointer was useful for debugging, but otherwise, i don't
> > think it should be printed.
> 
> But this is the only information to identify the guest if may guest
> are running.

Can't you get to task_struct, then pid?

A kernel pointer to identify a task is really weird (and not consistent 
with the other tracepoints).

> >> +	TP_ARGS(kvm, address, pte),
> >> +
> >> +	TP_STRUCT__entry(
> >> +		__field(struct kvm *, kvm)
> >> +		__field(unsigned long, address)
> >> +		__field(unsigned long, pte)
> >> +	),
> >> +
> >> +	TP_fast_assign(
> >> +		__entry->kvm = kvm;
> >> +		__entry->address = address;
> >> +		__entry->pte = pte.pte;
> >> +	),
> >> +
> >> +	TP_printk("kvm %p address %lx pte %lx", __entry->kvm, __entry->address,
> >> +		  __entry->pte)
> > 
> > The pte bits can be spelled out? (see __print_symbolic).
> 
> This tracepoint is put in kvm.h which can be used on different architectures
> which have different pte decode. I will try to find a way to show more
> readable format.
> >>  	spin_lock(&kvm->mmu_lock);
> >>
> >> +	trace_kvm_mmu_notifier_clear_flush_young(kvm, address);
> >> +
> >>  	young = kvm_age_hva(kvm, address);
> >>  	if (young)
> >>  		kvm_flush_remote_tlbs(kvm);
> >> @@ -394,6 +407,9 @@ static int kvm_mmu_notifier_test_young(struct mmu_notifier *mn,
> >>
> >>  	idx = srcu_read_lock(&kvm->srcu);
> >>  	spin_lock(&kvm->mmu_lock);
> >> +
> >> +	trace_kvm_mmu_notifier_test_young(kvm, address);
> >> +
> > 
> > can print young information?
> 
> Okay, will do it in next version.
> 
> Thanks for your review, Marcelo!
> 
> --
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