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SubjectRe: [PATCH 1/4] perf_counter: Default to higher paranoia level

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, 2009-08-21 at 16:21 +0200, Ingo Molnar wrote:
> > * Peter Zijlstra <peterz@infradead.org> wrote:
>
> > > diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
> > > index 9ba1822..2b0528f 100644
> > > --- a/include/linux/perf_counter.h
> > > +++ b/include/linux/perf_counter.h
> > > @@ -439,6 +439,7 @@ enum perf_callchain_context {
> > > struct perf_callchain_entry {
> > > __u64 nr;
> > > __u64 ip[PERF_MAX_STACK_DEPTH];
> > > + int restricted;
> > > };
> >
> > i'd love to have something more specific here - i.e. a context type
> > ID that identifies these basic types:
> >
> > - process
> > - softirq
> > - hardirq
> > - NMI
> >
> > and then let it be up to upper layers to decide what they do with a
> > restricted entry, and how to further process this information.
> >
> > And it's not just security: for example it would be interesting to
> > sample pure, non-irq overhead - as IRQ overhead is often unrelated
> > to the process being measured.
>
> Yes it is, this is purely about not showing some data. If you
> don't want to sample IRQ stuff that's something else, we'd have to
> grow that capability in hardware (like the OS/USR bits) or put
> perf enable/disable hooks into the irq entry/exit hooks (which
> doesn't sound all too hot an idea to me).
>
> Simply not showing the call-trace is something all-together
> different from not profiling it.

Well, it's not about not profiling it - it's about being able to
_separate out_ the samples from the various contexts.

Right now we already have context separators for call-chains:

PERF_CONTEXT_HV = (__u64)-32,
PERF_CONTEXT_KERNEL = (__u64)-128,
PERF_CONTEXT_USER = (__u64)-512,

PERF_CONTEXT_GUEST = (__u64)-2048,
PERF_CONTEXT_GUEST_KERNEL = (__u64)-2176,
PERF_CONTEXT_GUEST_USER = (__u64)-2560,

All i'm suggesting is to also have these context separators:

PERF_CONTEXT_KERNEL_HARDIRQ
PERF_CONTEXT_KERNEL_SOFTIRQ
PERF_CONTEXT_KERNEL /* syscall level */

So that if user-space wants to visualize just a portion of it, it
can do it.

Ingo


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