powerpc: tracing: Add powerpc tracepoints for interrupt entry and exit

This patch adds powerpc specific tracepoints for interrupt entry and exit.

While we already have generic irq_handler_entry and irq_handler_exit
tracepoints there are cases on our virtualised powerpc machines where an
interrupt is presented to the OS, but subsequently handled by the hypervisor.
This means no OS interrupt handler is invoked.

Here is an example on a POWER6 machine with the patch below applied:
 
<idle>-0     [006]  3243.949840744: irq_entry: pt_regs=c0000000ce31fb10
<idle>-0     [006]  3243.949850520: irq_exit: pt_regs=c0000000ce31fb10

<idle>-0     [007]  3243.950218208: irq_entry: pt_regs=c0000000ce323b10
<idle>-0     [007]  3243.950224080: irq_exit: pt_regs=c0000000ce323b10

<idle>-0     [000]  3244.021879320: irq_entry: pt_regs=c000000000a63aa0
<idle>-0     [000]  3244.021883616: irq_handler_entry: irq=87 handler=eth0
<idle>-0     [000]  3244.021887328: irq_handler_exit: irq=87 return=handled
<idle>-0     [000]  3244.021897408: irq_exit: pt_regs=c000000000a63aa0

Here we see two phantom interrupts (no handler was invoked), followed
by a real interrupt for eth0. Without the tracepoints in this patch we
would have missed the phantom interrupts.

Since these would be the first arch specific tracepoints, I'd like to make
sure we agree on naming. The tracepoints live in events/powerpc/*, but I'm
wondering if the tracepoint name should also contain the arch name, eg
powerpc_irq_entry/powerpc_irq_exit. Thoughts?

Signed-off-by: Anton Blanchard <anton@samba.org>
--

On Tue, 2009-10-06 at 13:19 +1100, Anton Blanchard wrote:
> This patch adds powerpc specific tracepoints for interrupt entry and exit.
> 
> While we already have generic irq_handler_entry and irq_handler_exit
> tracepoints there are cases on our virtualised powerpc machines where an
> interrupt is presented to the OS, but subsequently handled by the hypervisor.
> This means no OS interrupt handler is invoked.
> 
> Here is an example on a POWER6 machine with the patch below applied:

Hi Anton,

Thanks for the patch.

>  
> <idle>-0     [006]  3243.949840744: irq_entry: pt_regs=c0000000ce31fb10
> <idle>-0     [006]  3243.949850520: irq_exit: pt_regs=c0000000ce31fb10
> 
> <idle>-0     [007]  3243.950218208: irq_entry: pt_regs=c0000000ce323b10
> <idle>-0     [007]  3243.950224080: irq_exit: pt_regs=c0000000ce323b10
> 
> <idle>-0     [000]  3244.021879320: irq_entry: pt_regs=c000000000a63aa0
> <idle>-0     [000]  3244.021883616: irq_handler_entry: irq=87 handler=eth0
> <idle>-0     [000]  3244.021887328: irq_handler_exit: irq=87 return=handled
> <idle>-0     [000]  3244.021897408: irq_exit: pt_regs=c000000000a63aa0
> 
> Here we see two phantom interrupts (no handler was invoked), followed
> by a real interrupt for eth0. Without the tracepoints in this patch we
> would have missed the phantom interrupts.
> 
> Since these would be the first arch specific tracepoints, I'd like to make
> sure we agree on naming. The tracepoints live in events/powerpc/*, but I'm
> wondering if the tracepoint name should also contain the arch name, eg
> powerpc_irq_entry/powerpc_irq_exit. Thoughts?
> 
> Signed-off-by: Anton Blanchard <anton@samba.org>
> --
> 
> Index: linux.trees.git/arch/powerpc/kernel/irq.c
> ===================================================================
> --- linux.trees.git.orig/arch/powerpc/kernel/irq.c	2009-10-06 11:11:44.000000000 +1100
> +++ linux.trees.git/arch/powerpc/kernel/irq.c	2009-10-06 11:15:09.000000000 +1100
> @@ -54,6 +54,8 @@
>  #include <linux/pci.h>
>  #include <linux/debugfs.h>
>  #include <linux/perf_event.h>
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/powerpc.h>
>  
>  #include <asm/uaccess.h>
>  #include <asm/system.h>
> @@ -325,6 +327,8 @@ void do_IRQ(struct pt_regs *regs)
>  	struct pt_regs *old_regs = set_irq_regs(regs);
>  	unsigned int irq;
>  
> +	trace_irq_entry(regs);
> +
>  	irq_enter();
>  
>  	check_stack_overflow();
> @@ -348,6 +352,8 @@ void do_IRQ(struct pt_regs *regs)
>  		timer_interrupt(regs);
>  	}
>  #endif
> +
> +	trace_irq_exit(regs);
>  }
>  
>  void __init init_IRQ(void)
> Index: linux.trees.git/include/trace/events/powerpc.h
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ linux.trees.git/include/trace/events/powerpc.h	2009-10-06 11:14:05.000000000 +1100

I think this may do better in a file like:

arch/powerpc/kernel/trace.h

You can look at the sample code and Makefile in samples/trace_events/
that shows how to make it work outside the include/trace/events
directory.

I really would like to avoid placing arch specific files in a generic
directory, especially when there's a way to do it in the arch directory
itself.

This also contains the arch code a bit better.

Thanks,

-- Steve

> @@ -0,0 +1,47 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM powerpc
> +
> +#if !defined(_TRACE_POWERPC_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_POWERPC_H
> +
> +#include <linux/ptrace.h>
> +#include <linux/tracepoint.h>
> +
> +TRACE_EVENT(irq_entry,
> +
> +	TP_PROTO(struct pt_regs *regs),
> +
> +	TP_ARGS(regs),
> +
> +	TP_STRUCT__entry(
> +		__field(struct pt_regs *, regs)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->regs = regs;
> +	),
> +
> +	TP_printk("pt_regs=%p", __entry->regs)
> +);
> +
> +TRACE_EVENT(irq_exit,
> +
> +	TP_PROTO(struct pt_regs *regs),
> +
> +	TP_ARGS(regs),
> +
> +	TP_STRUCT__entry(
> +		__field(struct pt_regs *, regs)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->regs = regs;
> +	),
> +
> +	TP_printk("pt_regs=%p", __entry->regs)
> +);
> +
> +#endif /* _TRACE_POWERPC_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>