Re: [PATCH 02/32] tracing: Reimplement log2

Tom Zanussi
2017-07-14T16:13:30Z

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@linux.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);
> > }