Re: [tip:perfcounters/core] perf record/report: Add call graph / call chain profiling

Ingo Molnar
2009-06-16T08:10:09Z

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> > @@ -43,11 +44,19 @@ static int full_paths;
> > static unsigned long page_size;
> > static unsigned long mmap_window = 32;
> >
> > +struct ip_chain_event {
> > + __u16 nr;
>
> Is it needed to have the nr encoded in the ip_chain? We can
> already find it by doing kernel + user.

That's a good observation. Since we havent exposed the call-chain
bits in upstream version of the tools, we could still improve on
this a little bit.

I think the best would be context separators which occupy a special
address in some quiet corner of the 64-bit address space.

That way we'd have streams of u64 entries:

ip-1
ip-2
CONTEXT_IRQ
ip-3
ip-4
CONTEXT_SYSCALL
ip-5
ip-6

The following contexts IDs would be useful:

CONTEXT_NMI
CONTEXT_HARDIRQ
CONTEXT_SOFTIRQ
CONTEXT_KERNEL
CONTEXT_USER
CONTEXT_GUEST_NMI
CONTEXT_GUEST_HARDIRQ
CONTEXT_GUEST_SOFTIRQ
CONTEXT_GUEST_KERNEL
CONTEXT_GUEST_USER

The context IDs would occupy some rare and
unlikely-to-be-allocated-soon corner of the address space - say
startig at 0x8765432112345000. (and real RIPs would be filtered and
nudged just outside that space of a handful IDs.)

The advantage would be that this is infinitely flexible and
extensible - any level of nesting can be expressed without having
separate fields for nr_hv_guest_irq, etc. It's also pretty fast to
parse.

Hm?

Ingo