From: Avi Kivity <avi@redhat.com>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>, kvm <kvm@vger.kernel.org>
Subject: Re: kvm mmu tracing quirks
Date: Wed, 13 Apr 2011 19:12:35 +0300 [thread overview]
Message-ID: <4DA5CB73.3050202@redhat.com> (raw)
In-Reply-To: <4DA5AEAB.6020203@siemens.com>
On 04/13/2011 05:09 PM, Jan Kiszka wrote:
> Hi Xiao,
>
> while tracing a guest with all events enabled, I notices some issues
> with kvm mmu instrumentations. A critical one:
>
> TRACE_EVENT(
> kvm_mmu_audit,
> TP_PROTO(struct kvm_vcpu *vcpu, int audit_point),
> TP_ARGS(vcpu, audit_point),
>
> TP_STRUCT__entry(
> __field(struct kvm_vcpu *, vcpu)
> __field(int, audit_point)
> ),
>
> TP_fast_assign(
> __entry->vcpu = vcpu;
> __entry->audit_point = audit_point;
> ),
>
> TP_printk("vcpu:%d %s", __entry->vcpu->cpu,
> audit_point_name[__entry->audit_point])
> );
>
> Saving the vcpu reference to the trace buffer can break on dump if the
> vcpu was destroyed in the meantime. I was about to fix that by saving
> vcpu->cpu instead, but then I wondered what kind of information you
> actually need here. The triggering host cpu is automatically recorded by
> ftrace anyway. Can you comment on this / clean it up? Also, it would be
> nice to use __print_symbolic for translating audit_point to a string as
> that would also work for trace-cmd/kernelshark.
>
IIRC the audit trace is only used to get a low cost invocation for the
audit machinery; it's not actually useful as a user tracepoint.
We should probably switch to static_branch() instead
(https://lwn.net/Articles/429447/).
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2011-04-13 16:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-13 14:09 kvm mmu tracing quirks Jan Kiszka
2011-04-13 16:12 ` Avi Kivity [this message]
2011-04-14 3:47 ` Xiao Guangrong
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