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

Steven Rostedt
2009-03-25T15:43:57Z

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.

>
> 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.

-- Steve