Messages in this thread | | | Date | Fri, 27 Jan 2012 18:02:04 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 2/7] ftrace: Add enable/disable ftrace_ops control interface |
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On Fri, Jan 27, 2012 at 05:54:16PM +0100, Jiri Olsa wrote: > On Fri, Jan 27, 2012 at 05:40:49PM +0100, Frederic Weisbecker wrote: > > On Fri, Jan 27, 2012 at 11:37:14AM +0100, Jiri Olsa wrote: > > > On Thu, Jan 26, 2012 at 03:37:29AM +0100, Frederic Weisbecker wrote: > > > > On Wed, Jan 25, 2012 at 06:13:41PM -0500, Steven Rostedt wrote: > > > > > On Fri, 2012-01-20 at 18:02 +0100, Frederic Weisbecker wrote: > > > > > > > > > > > > > +/** > > > > > > > + * ftrace_function_enable - enable controlled ftrace_ops on given cpu > > > > > > > + * > > > > > > > + * This function enables tracing on given cpu by decreasing > > > > > > > + * the per cpu control variable. > > > > > > > + * It must be called with preemption disabled and only on > > > > > > > + * ftrace_ops registered with FTRACE_OPS_FL_CONTROL. > > > > > > > + */ > > > > > > > +static inline void ftrace_function_enable(struct ftrace_ops *ops, int cpu) > > > > > > > +{ > > > > > > > + atomic_t *disabled; > > > > > > > + > > > > > > > + if (WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_CONTROL) || > > > > > > > + !preempt_count())) > > > > > > > + return; > > > > > > > + > > > > > > > + disabled = per_cpu_ptr(ops->disabled, cpu); > > > > > > > + atomic_dec(disabled); > > > > > > > +} > > > > > > > > > > > > As you're using this for the local CPU exclusively, I suggest you rather > > > > > > rename it to "ftrace_function_{dis,en}able_cpu(struct ftrace_ops *ops)" > > > > > > > > > > I wonder if "ftrace_function_local_{dis,en}able(ops)" would be better? > > > > > That would match something like local_irq_disable/enable. > > > > > > > > Good idea. > > > > > > > > > > > > > > > and use __get_cpu_var() that does the preempt check for you. > > > > > > I haven't found preempt check this_cpu_ptr path.. not sure I missed it.. > > > so I'm keeping the implicit preemt check. > > > > #ifdef CONFIG_DEBUG_PREEMPT > > #define my_cpu_offset per_cpu_offset(smp_processor_id()) > > #else > > #define my_cpu_offset __my_cpu_offset > > #endif > > > > #ifdef CONFIG_DEBUG_PREEMPT > > #define this_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, my_cpu_offset) > > #else > > #define this_cpu_ptr(ptr) __this_cpu_ptr(ptr) > > #endif > > > > And smp_processor_id() has a preemption check. > > yay.. ok :) so this one is triggered only if there's CONFIG_DEBUG_PREEMPT > option enabled.. seems to me it'd better to keep the implicit check anyway. > > jirka
This is a debugging option deemed to lower runtime debugging checks in production.
Is there a good reason to keep the check on every case?
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