linux-kernel - Re: [PATCHv2 2/2] tracing,mm - add kernel pagefault tracepoint for x86 & x86

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Date:	Tue, 16 Nov 2010 10:23:06 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>, mingo@...e.hu,
	andi@...stfloor.org, lwoodman@...hat.com, hch@...radead.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCHv2 2/2] tracing,mm - add kernel pagefault tracepoint for
 x86 & x86_64

On Mon, Nov 15, 2010 at 09:19:20AM -0500, Steven Rostedt wrote:
> On Mon, 2010-11-15 at 14:43 +0100, Frederic Weisbecker wrote:
> 
> 
> > dotraplinkage void __kprobes
> > do_page_fault(struct pt_regs *regs, unsigned long error_code)
> > {
> > 	unsigned long address;
> > 
> > 	/* Get the faulting address: */
> > 	address = read_cr2();
> > 
> > 	trace_mm_pagefault_start(address, error_code);
> > 	__do_page_fault(regs, address, error_code);
> > 	trace_mm_pagefault_end(address);
> > }
> > 
> > 
> > Would you be ok with that?
> > 
> > Last thing I worry about is that error_code that is very arch dependent.
> > If someone writes a script that depends on the x86 code, it won't work
> > elsewhere while it's fairly possible to have a generic tracepoint there.
> > 
> > So perhaps we rather need a generic enum field instead of the error_code,
> > to express the most interesting specific fault attributes. Than can
> > probably be added later though, once someone really needs it.
> > 
> > Hm?
> 
> Perhaps we should have:
> 
> 	trace_arch_mm_pagefault_start(address, error_code);
> 	__do_page_fault(regs, address, error_code);
> 	trace_mm_pagefault_end(address);
> 
> 
> Then we have a arch/x86/kernel/trace.c that can map trace_arch_...
> events to generic events. This file will hold the
> trace_mm_pagefault_start(), which is called by
> trace_arch_mm_pagefault_start(). Have a hook that when the
> trace_mm_pagefault_start() is enabled, we also enable
> trace_arch_mm_pagefault_start() that calls this tracepoint. The
> trace_mm_pagefault_start() will then translate the
> trace_arch_mm_pagfault_start() into the generic trace_mm_pagefault_start
> event with the generic error_code that all archs will use.
> 
> Reason being, we don't need to do any extra processing in the fast path
> when tracing is not enabled.
> 
> Also, I'm going to start working on the stable ABI today.
do you mean stable api for the hook you described above?
or should I come up with smth..

thanks,
jirka
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