[RFC,v2,05/20] tracing/filters: Optimise cpumask vs cpumask filtering when user mask is a single CPU

Commit Message

Valentin Schneider July 20, 2023, 4:30 p.m. UTC

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.

Reuse do_filter_scalar_cpumask() when the input mask has a weight of one.

Suggested-by: Steven Rostedt <[e-mail]>
Signed-off-by: Valentin Schneider <[e-mail]>
---
 kernel/trace/trace_events_filter.c | 35 +++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

Comments

Steven Rostedt July 29, 2023, 7:34 p.m. UTC | #1

On Thu, 20 Jul 2023 17:30:41 +0100
Valentin Schneider <[e-mail]> wrote:

>  		/* Move along */
>  		i++;
> +
> +		/*
> +		 * Optimisation: if the user-provided mask has a weight of one
> +		 * then we can treat it as a scalar input.
> +		 */
> +		single = cpumask_weight(pred->mask) == 1;
> +		if (single && field->filter_type == FILTER_CPUMASK) {
> +			pred->val = cpumask_first(pred->mask);
> +			kfree(pred->mask);

Don't we need:
			pred->mask = NULL;

here, or the free_predicate() will cause a double free?

-- Steve

> +		}
> +

Valentin Schneider July 31, 2023, 11:20 a.m. UTC | #2

On 29/07/23 15:34, Steven Rostedt wrote:
> On Thu, 20 Jul 2023 17:30:41 +0100
> Valentin Schneider <[e-mail]> wrote:
>
>>              /* Move along */
>>              i++;
>> +
>> +		/*
>> +		 * Optimisation: if the user-provided mask has a weight of one
>> +		 * then we can treat it as a scalar input.
>> +		 */
>> +		single = cpumask_weight(pred->mask) == 1;
>> +		if (single && field->filter_type == FILTER_CPUMASK) {
>> +			pred->val = cpumask_first(pred->mask);
>> +			kfree(pred->mask);
>
> Don't we need:
>                       pred->mask = NULL;
>
> here, or the free_predicate() will cause a double free?
>

We do, thanks for spotting this.

> -- Steve
>
>> +		}
>> +

Patch

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 3009d0c61b532..2fe65ddeb34ef 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -70,6 +70,7 @@  enum filter_pred_fn {
 	FILTER_PRED_FN_CPU,
 	FILTER_PRED_FN_CPU_CPUMASK,
 	FILTER_PRED_FN_CPUMASK,
+	FILTER_PRED_FN_CPUMASK_CPU,
 	FILTER_PRED_FN_FUNCTION,
 	FILTER_PRED_FN_,
 	FILTER_PRED_TEST_VISITED,
@@ -957,6 +958,22 @@  static int filter_pred_cpumask(struct filter_pred *pred, void *event)
 	return do_filter_cpumask(pred->op, mask, cmp);
 }
 
+/* Filter predicate for cpumask field vs user-provided scalar  */
+static int filter_pred_cpumask_cpu(struct filter_pred *pred, void *event)
+{
+	u32 item = *(u32 *)(event + pred->offset);
+	int loc = item & 0xffff;
+	const struct cpumask *mask = (event + loc);
+	unsigned int cpu = pred->val;
+
+	/*
+	 * This inverts the usual usage of the function (field is first element,
+	 * user parameter is second), but that's fine because the (scalar, mask)
+	 * operations used are symmetric.
+	 */
+	return do_filter_scalar_cpumask(pred->op, cpu, mask);
+}
+
 /* Filter predicate for COMM. */
 static int filter_pred_comm(struct filter_pred *pred, void *event)
 {
@@ -1453,6 +1470,8 @@  static int filter_pred_fn_call(struct filter_pred *pred, void *event)
 		return filter_pred_cpu_cpumask(pred, event);
 	case FILTER_PRED_FN_CPUMASK:
 		return filter_pred_cpumask(pred, event);
+	case FILTER_PRED_FN_CPUMASK_CPU:
+		return filter_pred_cpumask_cpu(pred, event);
 	case FILTER_PRED_FN_FUNCTION:
 		return filter_pred_function(pred, event);
 	case FILTER_PRED_TEST_VISITED:
@@ -1666,6 +1685,7 @@  static int parse_pred(const char *str, void *data,
 
 	} else if (!strncmp(str + i, "CPUS", 4)) {
 		unsigned int maskstart;
+		bool single;
 		char *tmp;
 
 		switch (field->filter_type) {
@@ -1724,8 +1744,21 @@  static int parse_pred(const char *str, void *data,
 
 		/* Move along */
 		i++;
+
+		/*
+		 * Optimisation: if the user-provided mask has a weight of one
+		 * then we can treat it as a scalar input.
+		 */
+		single = cpumask_weight(pred->mask) == 1;
+		if (single && field->filter_type == FILTER_CPUMASK) {
+			pred->val = cpumask_first(pred->mask);
+			kfree(pred->mask);
+		}
+
 		if (field->filter_type == FILTER_CPUMASK) {
-			pred->fn_num = FILTER_PRED_FN_CPUMASK;
+			pred->fn_num = single ?
+				FILTER_PRED_FN_CPUMASK_CPU :
+				FILTER_PRED_FN_CPUMASK;
 		} else if (field->filter_type == FILTER_CPU) {
 			pred->fn_num = FILTER_PRED_FN_CPU_CPUMASK;
 		} else {