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

Namhyung Kim
2017-07-14T02:33:25Z

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' ?

Thanks,
Namhyung

> +
> kfree(hist_field);
> }