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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Date:   Mon, 31 Jul 2023 12:20:41 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
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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 29/07/23 15:55, Steven Rostedt wrote:
> 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;
>

That's neater, thanks!

> -- 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: