Messages in this thread Patch in this message |  | | Date | Thu, 4 Feb 2021 14:52:51 -0500 (EST) | From | Mathieu Desnoyers <> | Subject | Re: [PATCH] tracepoints: Do not punish non static call users |
| |
----- On Feb 4, 2021, at 2:17 PM, rostedt rostedt@goodmis.org wrote:
> With static calls, a tracepoint can call the callback directly if there is > only one callback registered to that tracepoint. When there is more than > one, the static call will call the tracepoint's "iterator" function, which > needs to reload the tracepoint's "funcs" array again, as it could have > changed since the first time it was loaded. > > But an arch without static calls is punished by having to load the > tracepoint's "funcs" array twice. Once in the DO_TRACE macro, and once > again in the iterator macro.
In addition to loading it, it needs to test it against NULL twice.
> > For archs without static calls, there's no reason to load the array macro > in the first place, since the iterator function will do it anyway. > > Change the __DO_TRACE_CALL() macro to do the double call only for
Do you mean "double call" or "double load and NULL check" ?
> architectures with static calls, and just call the iterator function > directly for architectures without static calls. > > [ Tested only on architectures with static calls, will test on those > without later ] > > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> > --- > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h > index dc1d4c612cc3..966bfa6a861c 100644 > --- a/include/linux/tracepoint.h > +++ b/include/linux/tracepoint.h > @@ -152,9 +152,18 @@ static inline struct tracepoint > *tracepoint_ptr_deref(tracepoint_ptr_t *p) > #ifdef TRACEPOINTS_ENABLED > > #ifdef CONFIG_HAVE_STATIC_CALL > -#define __DO_TRACE_CALL(name) static_call(tp_func_##name) > +#define __DO_TRACE_CALL(name, args) \ > + do { \ > + struct tracepoint_func *it_func_ptr; \ > + it_func_ptr = \ > + rcu_dereference_raw((&__tracepoint_##name)->funcs); \ > + if (it_func_ptr) { \ > + __data = (it_func_ptr)->data; \ > + static_call(tp_func_##name)(args); \ > + } \ > + } while (0) > #else > -#define __DO_TRACE_CALL(name) __traceiter_##name > +#define __DO_TRACE_CALL(name, args) __traceiter_##name(args)
Also, we may want to comment or annotate the "void *data" argument of __traceiter_##_name() to state that it is unused.
Thanks,
Mathieu
> #endif /* CONFIG_HAVE_STATIC_CALL */ > > /* > @@ -168,7 +177,6 @@ static inline struct tracepoint > *tracepoint_ptr_deref(tracepoint_ptr_t *p) > */ > #define __DO_TRACE(name, proto, args, cond, rcuidle) \ > do { \ > - struct tracepoint_func *it_func_ptr; \ > int __maybe_unused __idx = 0; \ > void *__data; \ > \ > @@ -190,12 +198,7 @@ static inline struct tracepoint > *tracepoint_ptr_deref(tracepoint_ptr_t *p) > rcu_irq_enter_irqson(); \ > } \ > \ > - it_func_ptr = \ > - rcu_dereference_raw((&__tracepoint_##name)->funcs); \ > - if (it_func_ptr) { \ > - __data = (it_func_ptr)->data; \ > - __DO_TRACE_CALL(name)(args); \ > - } \ > + __DO_TRACE_CALL(name, TP_ARGS(args)); \ > \ > if (rcuidle) { \ > rcu_irq_exit_irqson(); \
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
|  |