Re: [PATCH v9 3/3] trace,x86: code-sharing between non-trace and trace irq handlers

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 2013-02-15 at 16:13 -0800, H. Peter Anvin wrote:

> How important is it that the tracepoint is *inside* the enter/exit
> handling?  If not, it would be simpler to just do:
> 
> smp_trace_irq_handler()
> {
> 	trace_irq_entry();
> 	smp_irq_handler();
> 	trace_irq_exit();
> }
> 
> ... which seems a bit cleaner.  If this isn't possible, then this patch
> is fine, but please add to the patch description why the simple wrapper
> isn't doable.

The problem is with irq_enter/exit() being called. They must be called
before trace_irq_enter/exit(), because of the rcu_irq_enter() must be
called before any tracepoints are used, as tracepoints use rcu to
synchronize.

Now perhaps we could do this and have trace_irq_entry().

Not only that, the tracepoint callbacks expect irq_enter() to already be
called.

Hmm, if irq_enter() can nest, which I think it can, perhaps we can call
irq_enter() first. I'm not sure if that will screw up the second
irq_entry() inside smp_irq_handler().

smp_trace_irq_hander()
{
	irq_entry();
	trace_irq_entry();
	smp_irq_handler();
	trace_irq_exit();
	irq_exit();
}

-- Steve