linux-kernel - [RFC PATCH 3/7] trace: Optimize trace_get_context

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Date:   Tue,  2 Apr 2019 22:03:55 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        Romulo Silva de Oliveira <romulo.deoliveira@...c.br>,
        Clark Williams <williams@...hat.com>, x86@...nel.org
Subject: [RFC PATCH 3/7] trace: Optimize trace_get_context_bit()

trace_get_context_bit() and trace_recursive_lock() uses the same logic,
but the second reads the per_cpu variable only once.

Uses the trace_recursive_lock()'s logic in trace_get_context_bit().

Signed-off-by: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>
Cc: Romulo Silva de Oliveira <romulo.deoliveira@...c.br>
Cc: Clark Williams <williams@...hat.com>
Cc: linux-kernel@...r.kernel.org
Cc: x86@...nel.org
---
 kernel/trace/trace.h | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index dad2f0cd7208..09318748fab8 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -635,20 +635,13 @@ enum {
 
 static __always_inline int trace_get_context_bit(void)
 {
-	int bit;
-
-	if (in_interrupt()) {
-		if (in_nmi())
-			bit = TRACE_CTX_NMI;
+	unsigned long pc = preempt_count();
 
-		else if (in_irq())
-			bit = TRACE_CTX_IRQ;
-		else
-			bit = TRACE_CTX_SOFTIRQ;
-	} else
-		bit = TRACE_CTX_NORMAL;
-
-	return bit;
+	if (pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET))
+		return pc & NMI_MASK ? TRACE_CTX_NMI :
+			pc & HARDIRQ_MASK ? TRACE_CTX_IRQ : TRACE_CTX_SOFTIRQ;
+	else
+		return TRACE_CTX_NORMAL;
 }
 
 static __always_inline int trace_test_and_set_recursion(int start, int max)
-- 
2.20.1