linux-kernel - [tip:perf/core] perf/x86: Micro-optimize nhmex_rbox_get

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Message-ID: <tip-2172c1f5aa58310784f358ca20fdddfcdc2a0d7b@git.kernel.org>
Date:	Sat, 5 Jul 2014 03:47:08 -0700
From:	tip-bot for Rasmus Villemoes <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, linux@...musvillemoes.dk,
	hpa@...or.com, mingo@...nel.org, peterz@...radead.org,
	acme@...nel.org, tglx@...utronix.de
Subject: [tip:perf/core] perf/x86:
  Micro-optimize nhmex_rbox_get_constraint()

Commit-ID:  2172c1f5aa58310784f358ca20fdddfcdc2a0d7b
Gitweb:     http://git.kernel.org/tip/2172c1f5aa58310784f358ca20fdddfcdc2a0d7b
Author:     Rasmus Villemoes <linux@...musvillemoes.dk>
AuthorDate: Thu, 19 Jun 2014 15:15:31 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sat, 5 Jul 2014 11:21:52 +0200

perf/x86: Micro-optimize nhmex_rbox_get_constraint()

Flipping the LSB doesn't require four lines of code. This shaves a few
bytes of the generated code, including a branch.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/r/1403183731-15402-1-git-send-email-linux@rasmusvillemoes.dk
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/cpu/perf_event_intel_uncore.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore.c b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
index 65bbbea..e009f3c 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_uncore.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
@@ -2946,10 +2946,7 @@ again:
 		 * extra registers. If we failed to take an extra
 		 * register, try the alternative.
 		 */
-		if (idx % 2)
-			idx--;
-		else
-			idx++;
+		idx ^= 1;
 		if (idx != reg1->idx % 6) {
 			if (idx == 2)
 				config1 >>= 8;
--
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