linux-kernel - [tip: perf/urgent] perf: Optimize get_recursion

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Date:   Tue, 10 Nov 2020 12:45:21 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf: Optimize get_recursion_context()

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     09da9c81253dd8e43e0d2d7cea02de6f9f19499d
Gitweb:        https://git.kernel.org/tip/09da9c81253dd8e43e0d2d7cea02de6f9f19499d
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Fri, 30 Oct 2020 13:43:16 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 09 Nov 2020 18:12:34 +01:00

perf: Optimize get_recursion_context()

  "Look ma, no branches!"

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>
Link: https://lkml.kernel.org/r/20201030151955.187580298@infradead.org
---
 kernel/events/internal.h | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 402054e..228801e 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -205,16 +205,12 @@ DEFINE_OUTPUT_COPY(__output_copy_user, arch_perf_out_copy_user)
 
 static inline int get_recursion_context(int *recursion)
 {
-	int rctx;
-
-	if (unlikely(in_nmi()))
-		rctx = 3;
-	else if (in_irq())
-		rctx = 2;
-	else if (in_serving_softirq())
-		rctx = 1;
-	else
-		rctx = 0;
+	unsigned int pc = preempt_count();
+	unsigned char rctx = 0;
+
+	rctx += !!(pc & (NMI_MASK));
+	rctx += !!(pc & (NMI_MASK | HARDIRQ_MASK));
+	rctx += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));
 
 	if (recursion[rctx])
 		return -1;