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.

Link: https://lkml.kernel.org/r/20230707172155.70873-6-vschneid@redhat.com
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Leonardo Bras <leobras@redhat.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 3009d0c61b532c1e3314df66c248e85162ff143c..2fe65ddeb34efb614264255b8bd5e8ba8f8ef4fe 100644 (file)
--- 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 {