Re: [PATCH 2/5][RFC] tracing: move function profiler data out of function struct

Ingo Molnar
2009-03-25T17:45:42Z

* Steven Rostedt <rostedt@goodmis.org> wrote:

>
> On Wed, 25 Mar 2009, Ingo Molnar wrote:
>
> >
> > * Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > > +/* Interrupts must be disabled calling this */
> > > +static struct ftrace_profile *
> > > +ftrace_profile_alloc(unsigned long ip, bool alloc_safe)
> > > +{
> > > + struct ftrace_profile *rec = NULL;
> > > +
> > > + /* prevent recursion */
> > > + if (atomic_inc_return(&__get_cpu_var(ftrace_profile_disable)) != 1)
> > > + goto out;
> > > +
> > > + __raw_spin_lock(&ftrace_profile_rec_lock);
> > > +
> > > + /* Try to always keep another page available */
> > > + if (!profile_pages->next && alloc_safe)
> > > + profile_pages->next = (void *)get_zeroed_page(GFP_ATOMIC);
> >
> > this does not seem to be NMI safe.
>
> The atomic_inc_return protects against NMIs, since this is the only place
> the lock is taken.

i mean, if this code executes _ni_ an NMI. Or that cannot happen? We
trace nmis too, dont we?

> > This all would be solved much more robustly by the function
> > attributes hash approach i suggested in the previous mail. If
> > percpu_alloc() is done for 20,000 functions the memory
> > allocation overhead is no big deal.
>
> Later patches create a per-cpu buffers and removes the lock.

ok :)

Ingo