linux-kernel - Re: [RFC][PATCH v2] tracing: Add __bitmask() macro to trace events to cpumasks and other bitmasks

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Date:	Wed, 14 May 2014 11:36:23 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Javi Merino <javi.merino@....com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [RFC][PATCH v2] tracing: Add __bitmask() macro to trace events
 to cpumasks and other bitmasks

On Wed, 14 May 2014 15:23:24 +0100
Javi Merino <javi.merino@....com> wrote:

> > diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> > index 0a1a4f7..d9c44af 100644
> > --- a/include/trace/ftrace.h
> > +++ b/include/trace/ftrace.h
> > @@ -53,6 +53,9 @@
> >  #undef __string
> >  #define __string(item, src) __dynamic_array(char, item, -1)
> >  
> > +#undef __bitmask
> > +#define __bitmask(item, src) __dynamic_array(char, item, -1)
> > +
> >  #undef TP_STRUCT__entry
> >  #define TP_STRUCT__entry(args...) args
> >  
> > @@ -128,6 +131,9 @@
> >  #undef __string
> >  #define __string(item, src) __dynamic_array(char, item, -1)
> >  
> > +#undef __string
> > +#define __string(item, src) __dynamic_array(unsigned long, item, -1)
> > +
> 
> This overrides the previous definition of __string() and looks like it
> shouldn't be here.

Bah! I knew there was a reason I didn't push this out to my for-next
branch yet. I can still rebase :-)

That should have been __bitmask(). Hmm, amazing it still worked.

> 
> >  #undef DECLARE_EVENT_CLASS
> >  #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
> >  	struct ftrace_data_offsets_##call {				\
> > @@ -200,6 +206,15 @@
> >  #undef __get_str
> >  #define __get_str(field) (char *)__get_dynamic_array(field)
> >  
> > +#undef __get_bitmask
> > +#define __get_bitmask(field)						\
> > +	({								\
> > +		void *__bitmask = __get_dynamic_array(field);		\
> > +		unsigned int __bitmask_size;				\
> > +		__bitmask_size = (__entry->__data_loc_##field >> 16) & 0xffff; \
> > +		ftrace_print_bitmask_seq(p, __bitmask, __bitmask_size);	\
> > +	})
> > +
> >  #undef __print_flags
> >  #define __print_flags(flag, delim, flag_array...)			\
> >  	({								\
> > @@ -322,6 +337,9 @@ static struct trace_event_functions ftrace_event_type_funcs_##call = {	\
> >  #undef __string
> >  #define __string(item, src) __dynamic_array(char, item, -1)
> >  
> > +#undef __bitmask
> > +#define __bitmask(item, src) __dynamic_array(unsigned long, item, -1)
> > +
> >
> >  #undef DECLARE_EVENT_CLASS
> >  #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, func, print)	\
> >  static int notrace __init						\
> > @@ -372,6 +390,29 @@ ftrace_define_fields_##call(struct ftrace_event_call *event_call)	\
> >  #define __string(item, src) __dynamic_array(char, item,			\
> >  		    strlen((src) ? (const char *)(src) : "(null)") + 1)
> >  
> > +/*
> > + * __bitmask_size_in_bytes_raw is the number of bytes needed to hold
> > + * num_possible_cpus().
> > + */
> > +#define __bitmask_size_in_bytes_raw			\
> > +	((num_possible_cpus() + 7) / 8)
> > +
> > +#define __bitmask_size_in_longs						\
> > +	((__bitmask_size_in_bytes_raw + ((BITS_PER_LONG / 8) - 1))	\
> > +	 / (BITS_PER_LONG / 8))
> > +
> > +/*
> > + * __bitmask_size_in_bytes is the number of bytes needed to hold
> > + * num_possible_cpus() padded out to the nearest long. This is what
> > + * is saved in the buffer, just to be consistent.
> > + */
> > +#define __bitmask_size_in_bytes				\
> > +	(__bitmask_size_in_longs * (BITS_PER_LONG / 8))
> > +
> > +#undef __bitmask
> > +#define __bitmask(item, src) __dynamic_array(unsigned long, item,	\
> > +					     __bitmask_size_in_longs)
> > +
> >  #undef DECLARE_EVENT_CLASS
> >  #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
> >  static inline notrace int ftrace_get_offsets_##call(			\
> > @@ -513,12 +554,22 @@ static inline notrace int ftrace_get_offsets_##call(			\
> >  	__entry->__data_loc_##item = __data_offsets.item;
> >  
> >  #undef __string
> > -#define __string(item, src) __dynamic_array(char, item, -1)       	\
> > +#define __string(item, src) __dynamic_array(char, item, -1)
> >  
> >  #undef __assign_str
> >  #define __assign_str(dst, src)						\
> >  	strcpy(__get_str(dst), (src) ? (const char *)(src) : "(null)");
> >  
> > +#undef __bitmask
> > +#define __bitmask(item, src) __dynamic_array(unsigned long, item, -1)
> 
> Why src?  It's not used in any of the definitions of the __bitmask()
> macro, can we remove it?

Hmm, I may need to refactor this. I may pull this patch for now to push
the rest to for-next.

I just noticed that we need a way to specify the length of the bitmask.
Right now it's hardcoded as "num_possible_cpus", which Mathieu was
asking for a more generic approach.

OK, let me pull this patch out of my tree (thank god I never pushed
it), and work on it a bit more.

Thanks,

-- Steve

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