linux-kernel - Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer

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Date:	Fri, 03 Apr 2009 15:17:06 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Masami Hiramatsu <mhiramat@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Jim Keniston <jkenisto@...ibm.com>, kvm@...r.kernel.org,
	systemtap-ml <systemtap@...rces.redhat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer

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.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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