linux-kernel - Re: [PATCH 02/32] tracing: Reimplement log2

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Date:   Fri, 14 Jul 2017 11:13:25 -0500
From:   Tom Zanussi <tom.zanussi@...ux.intel.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     rostedt@...dmis.org, tglx@...utronix.de, mhiramat@...nel.org,
        vedang.patel@...el.com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH 02/32] tracing: Reimplement log2

Hi Namhyung,

On Fri, 2017-07-14 at 11:33 +0900, Namhyung Kim wrote:
> On Mon, Jun 26, 2017 at 05:49:03PM -0500, Tom Zanussi wrote:
> > log2 as currently implemented applies only to u64 trace_event_field
> > derived fields, and assumes that anything it's applied to is a u64
> > field.
> > 
> > To prepare for synthetic fields like latencies, log2 should be
> > applicable to those as well, so take the opportunity now to fix the
> > current problems as well as expand to more general uses.
> > 
> > log2 should be thought of as a chaining function rather than a field
> > type.  To enable this as well as possible future function
> > implementations, add a hist_field operand array into the hist_field
> > definition for this purpose, and make use of it to implement the log2
> > 'function'.
> > 
> > Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> > ---
> >  kernel/trace/trace_events_hist.c | 31 +++++++++++++++++++++++++++----
> >  1 file changed, 27 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> > index 91ffc39..7b55956 100644
> > --- a/kernel/trace/trace_events_hist.c
> > +++ b/kernel/trace/trace_events_hist.c
> > @@ -28,12 +28,16 @@
> >  
> >  typedef u64 (*hist_field_fn_t) (struct hist_field *field, void *event);
> >  
> > +#define HIST_FIELD_OPERANDS_MAX	2
> > +
> >  struct hist_field {
> >  	struct ftrace_event_field	*field;
> >  	unsigned long			flags;
> >  	hist_field_fn_t			fn;
> >  	unsigned int			size;
> >  	unsigned int			offset;
> > +	unsigned int                    is_signed;
> > +	struct hist_field		*operands[HIST_FIELD_OPERANDS_MAX];
> >  };
> >  
> >  static u64 hist_field_none(struct hist_field *field, void *event)
> > @@ -71,7 +75,9 @@ static u64 hist_field_pstring(struct hist_field *hist_field, void *event)
> >  
> >  static u64 hist_field_log2(struct hist_field *hist_field, void *event)
> >  {
> > -	u64 val = *(u64 *)(event + hist_field->field->offset);
> > +	struct hist_field *operand = hist_field->operands[0];
> > +
> > +	u64 val = operand->fn(operand, event);
> >  
> >  	return (u64) ilog2(roundup_pow_of_two(val));
> >  }
> > @@ -156,6 +162,8 @@ static const char *hist_field_name(struct hist_field *field,
> >  
> >  	if (field->field)
> >  		field_name = field->field->name;
> > +	else if (field->flags & HIST_FIELD_FL_LOG2)
> > +		field_name = hist_field_name(field->operands[0], ++level);
> >  
> >  	if (field_name == NULL)
> >  		field_name = "";
> > @@ -357,8 +365,20 @@ static void hist_trigger_elt_comm_init(struct tracing_map_elt *elt)
> >  	.elt_init	= hist_trigger_elt_comm_init,
> >  };
> >  
> > -static void destroy_hist_field(struct hist_field *hist_field)
> > +static void destroy_hist_field(struct hist_field *hist_field,
> > +			       unsigned int level)
> >  {
> > +	unsigned int i;
> > +
> > +	if (level > 2)
> > +		return;
> > +
> > +	if (!hist_field)
> > +		return;
> > +
> > +	for (i = 0; i < HIST_FIELD_OPERANDS_MAX; i++)
> > +		destroy_hist_field(hist_field->operands[i], ++level);
> 
> Wouldn't it be 'level + 1' ?
> 

Yeah, we're in a loop here, so definitely.  Thanks for catching this.

Tom

> Thanks,
> Namhyung
> 
> 
> > +
> >  	kfree(hist_field);
> >  }