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Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer
- From: Avi Kivity <avi at redhat dot com>
- To: Ingo Molnar <mingo at elte dot hu>
- 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, 03 Apr 2009 14:50:35 +0300
- Subject: Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer
- References: <49D4F4B5.9040107@redhat.com> <20090403112639.GC31399@elte.hu>
Ingo Molnar wrote:
ok, the structure and concept looks quite good now, really nice!
I'm wondering about something i suggested many moons ago: to look
into the KVM decoder+emulator (arch/x86/kvm/x86_emulate.c).
I remember there were some issues with that (one problem being that
the KVM decoder is a special-purpose thing covering specific range
of execution environments - not a near-full integer-ops decoder like
the one we are aiming for here) - are there any other fundamental
problems beyond 'it has to be done' ?
Conceptually we want just a single piece of decoder logic in
arch/x86/. If the KVM folks are cool with it we could factor out the
KVM one into arch/x86/lib/. But ... if there are compelling reasons
to leave the KVM one alone in its limited environment we can do that
too.
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.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.