linux-kernel - [PATCH 4/6] perf: Optimize get_recursion

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Date:   Fri, 30 Oct 2020 16:13:49 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, tglx@...utronix.de, rostedt@...dmis.org
Cc:     linux-kernel@...r.kernel.org, kan.liang@...ux.intel.com,
        acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, ak@...ux.intel.com, eranian@...gle.com,
        peterz@...radead.org, Jesper Dangaard Brouer <brouer@...hat.com>
Subject: [PATCH 4/6] perf: Optimize get_recursion_context()

  "Look ma, no branches!"

Cc: Jesper Dangaard Brouer <brouer@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/events/internal.h |   17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -205,16 +205,15 @@ DEFINE_OUTPUT_COPY(__output_copy_user, a
 
 static inline int get_recursion_context(int *recursion)
 {
-	int rctx;
+	unsigned int pc = preempt_count();
+	unsigned int rctx = 0;
 
-	if (unlikely(in_nmi()))
-		rctx = 3;
-	else if (in_irq())
-		rctx = 2;
-	else if (in_serving_softirq())
-		rctx = 1;
-	else
-		rctx = 0;
+	if (pc & (NMI_MASK))
+		rctx++;
+	if (pc & (NMI_MASK | HARDIRQ_MASK))
+		rctx++;
+	if (pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET))
+		rctx++;
 
 	if (recursion[rctx])
 		return -1;