Re: [RFC PATCH v2 06/20] tracing/filters: Optimise scalar vs cpumask filtering when the user mask is a single CPU

Steven Rostedt
2023-07-29T19:56:23Z

On Thu, 20 Jul 2023 17:30:42 +0100
Valentin Schneider <vschneid@redhat.com> wrote:

> Steven noted that when the user-provided cpumask contains a single CPU,
> then the filtering function can use a scalar as input instead of a
> full-fledged cpumask.
>
> When the mask contains a single CPU, directly re-use the unsigned field
> predicate functions. Transform '&' into '==' beforehand.
>
> Suggested-by: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Valentin Schneider <vschneid@redhat.com>
> ---
> kernel/trace/trace_events_filter.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> index 2fe65ddeb34ef..54d642fabb7f1 100644
> --- a/kernel/trace/trace_events_filter.c
> +++ b/kernel/trace/trace_events_filter.c
> @@ -1750,7 +1750,7 @@ static int parse_pred(const char *str, void *data,
> * then we can treat it as a scalar input.
> */
> single = cpumask_weight(pred->mask) == 1;
> - if (single && field->filter_type == FILTER_CPUMASK) {
> + if (single && field->filter_type != FILTER_CPU) {
> pred->val = cpumask_first(pred->mask);
> kfree(pred->mask);
> }
> @@ -1761,6 +1761,11 @@ static int parse_pred(const char *str, void *data,
> FILTER_PRED_FN_CPUMASK;
> } else if (field->filter_type == FILTER_CPU) {
> pred->fn_num = FILTER_PRED_FN_CPU_CPUMASK;
> + } else if (single) {
> + pred->op = pred->op == OP_BAND ? OP_EQ : pred->op;

Nit, the above can be written as:

pred->op = pret->op != OP_BAND ? : OP_EQ;

-- Steve

> + pred->fn_num = select_comparison_fn(pred->op, field->size, false);
> + if (pred->op == OP_NE)
> + pred->not = 1;
> } else {
> switch (field->size) {
> case 8: