linux-kernel - [RFC PATCH v2 08/20] tracing/filters: Further optimise scalar vs cpumask comparison

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Message-Id: <20230720163056.2564824-9-vschneid@redhat.com>
Date:   Thu, 20 Jul 2023 17:30:44 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
        bpf@...r.kernel.org, x86@...nel.org, rcu@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
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        Zqiang <qiang.zhang1211@...il.com>,
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        Christoph Hellwig <hch@...radead.org>,
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        Yair Podemsky <ypodemsk@...hat.com>
Subject: [RFC PATCH v2 08/20] tracing/filters: Further optimise scalar vs cpumask comparison

Per the previous commits, we now only enter do_filter_scalar_cpumask() with
a mask of weight greater than one. Optimise the equality checks.

Suggested-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Valentin Schneider <vschneid@...hat.com>
---
 kernel/trace/trace_events_filter.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index fd72dacc5d1b8..3a529214a21b7 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -667,6 +667,25 @@ do_filter_cpumask(int op, const struct cpumask *mask, const struct cpumask *cmp)
 /* Optimisation of do_filter_cpumask() for scalar fields */
 static inline int
 do_filter_scalar_cpumask(int op, unsigned int cpu, const struct cpumask *mask)
+{
+	/*
+	 * Per the weight-of-one cpumask optimisations, the mask passed in this
+	 * function has a weight >= 2, so it is never equal to a single scalar.
+	 */
+	switch (op) {
+	case OP_EQ:
+		return false;
+	case OP_NE:
+		return true;
+	case OP_BAND:
+		return cpumask_test_cpu(cpu, mask);
+	default:
+		return 0;
+	}
+}
+
+static inline int
+do_filter_cpumask_scalar(int op, const struct cpumask *mask, unsigned int cpu)
 {
 	switch (op) {
 	case OP_EQ:
@@ -966,12 +985,7 @@ static int filter_pred_cpumask_cpu(struct filter_pred *pred, void *event)
 	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);
+	return do_filter_cpumask_scalar(pred->op, mask, cpu);
 }
 
 /* Filter predicate for COMM. */
-- 
2.31.1