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Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer
- From: Ingo Molnar <mingo at elte dot hu>
- To: Avi Kivity <avi at redhat dot com>
- Cc: Masami Hiramatsu <mhiramat at redhat dot com>, "H. Peter Anvin" <hpa at zytor dot com>, Frederic Weisbecker <fweisbec at gmail dot com>, Steven Rostedt <rostedt at goodmis dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Andrew Morton <akpm at linux-foundation dot org>, Andi Kleen <andi at firstfloor dot org>, Jim Keniston <jkenisto at us dot ibm dot com>, kvm at vger dot kernel dot org, systemtap-ml <systemtap at sources dot redhat dot com>, LKML <linux-kernel at vger dot kernel dot org>
- Date: Fri, 3 Apr 2009 14:26:54 +0200
- Subject: Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer
- References: <49D4F4B5.9040107@redhat.com> <20090403112639.GC31399@elte.hu> <49D5F80B.7000305@redhat.com> <20090403121202.GI31399@elte.hu> <49D5FE42.5080100@redhat.com>
* Avi Kivity <avi@redhat.com> wrote:
> Ingo Molnar wrote:
>>> kvm has three requirements not needed by kprobes:
>>> - it wants to execute instructions, not just decode them, including
>>> generating faults where appropriate
>>> - it is performance critical
>>> - it needs to support 16-bit, 32-bit, and 64-bit instructions simultaneously
>>>
>>> If an arch/x86/ decoder/emulator gives me these I'll gladly switch
>>> to it. x86_emulate.c is high on my list of most disliked code.
>>>
>>
>> Well, this has to be driven from the KVM side as the kprobes use
>> will only be for decoding so if it's modified from the kprobes
>> side the KVM-only functionality might regress.
>>
>> So ... we can do the library decoder for kprobes purposes, and
>> someone versed in the KVM emulator can then combine the two.
>
> Problem is, anyone versed in the kvm emulator will want to run as
> far away from this work as possible.
Are you suggesting that the KVM emulator should never have been
merged in the first place? ;-)
Anyway, we'll make sure the kprobes/library decoder is as clean as
possible - so it ought to be hackable and extensible without the
risk of permanent brain damage. Mmiotrace and kmemcheck has decoding
smarts too, and i think the sw-breakpoint injection code of KGDB
could use it as well - so there's broader utility in all this.
Ingo