linux-kernel - [PATCH] x86: Micro-optimization in nhmex_rbox_get

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Message-Id: <1403183731-15402-1-git-send-email-linux@rasmusvillemoes.dk>
Date:	Thu, 19 Jun 2014 15:15:31 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH] x86: Micro-optimization in 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>
---
 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;
-- 
1.9.2

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