2023-07-20 16:40:00

by Valentin Schneider

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

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

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 {
--
2.31.1

2023-07-29 19:56:39

by Steven Rostedt

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

On Thu, 20 Jul 2023 17:30:41 +0100
Valentin Schneider <[email protected]> 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

> + }
> +

2023-07-31 12:18:50

by Valentin Schneider

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

On 29/07/23 15:34, Steven Rostedt wrote:
> On Thu, 20 Jul 2023 17:30:41 +0100
> Valentin Schneider <[email protected]> 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
>
>> + }
>> +