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

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Message-ID: <20230729155547.35719a1f@rorschach.local.home>
Date:   Sat, 29 Jul 2023 15:55:47 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Valentin Schneider <vschneid@...hat.com>
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Subject: Re: [RFC PATCH v2 06/20] tracing/filters: Optimise scalar vs
 cpumask filtering when the user mask is a single CPU

On Thu, 20 Jul 2023 17:30:42 +0100
Valentin Schneider <vschneid@...hat.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@...dmis.org>
> Signed-off-by: Valentin Schneider <vschneid@...hat.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: