linux-kernel - Re: [RFC][PATCH 2/2] tracing/x86: basic implementation of syscall tracing for x86-64

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Message-ID: <20090315192205.GA10131@Krystal>
Date:	Sun, 15 Mar 2009 15:22:05 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiaying Zhang <jiayingz@...gle.com>,
	Martin Bligh <mbligh@...gle.com>
Subject: Re: [RFC][PATCH 2/2] tracing/x86: basic implementation of syscall
	tracing for x86-64

* Ingo Molnar (mingo@...e.hu) wrote:
> 
> * Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > * Ingo Molnar (mingo@...e.hu) wrote:
> > > 
> > > * Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> > > 
> > > > * Frederic Weisbecker (fweisbec@...il.com) wrote:
> > > >
> > > > > Provide the ptrace hooks and arch specific syscall numbers 
> > > > > to ftrace arch indepedant syscall numbers. For now it only 
> > > > > supports 4 syscalls to provide an example.
> > > > > 
> > > > 
> > > > Hi Frederic,
> > > > 
> > > > I already have the equivalent TIF_KERNEL_TRACE flag in my 
> > > > LTTng tree added to every Linux architecture. You might want 
> > > > to re-use this work rather than re-doing this. I don't mind 
> > > > changing the flag name.
> > > 
> > > Yeah. Note that the TIF bits are just one part - there are other 
> > > bits needed for HAVE_FTRACE_SYSCALLS arch support.
> > > 
> > > Also, i'd eventually expect the TIF bits to be converted to a 
> > > tracehook callback, not spread it to other architectures.
> > > 
> > 
> > The nice part about the TIF bit is that it permits adding this 
> > syscall tracing feature without increasing the size of the 
> > thread_info struct nor adding any extra tests in entry.S. Does 
> > the tracehook callback have these features ?
> 
> yes. Tracehook just factors out common interfacing points - with 
> one specific implementation for now: ptrace. For syscall tracing 
> that means it wraps TIF_SYSCALL_TRACE in essence.
> 
> 	Ingo

What overhead and latency does tracehooks add when

- they are being enabled/disabled
- once they are enabled ?

Do they require to stop each and every thread upon activation ?

I'll post my lttng trace flags for RFC, as it could save Frederic some
duplicated work. Feel free to comment.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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