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authorRob Herring <rob.herring@calxeda.com>2012-11-29 20:39:54 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2012-12-03 11:16:36 +0000
commit14318efb322e2fe1a034c69463d725209eb9d548 (patch)
treecf99b8a06eca7abdb89ac87c7f35bebb6b3254f7 /arch/arm/include/asm/percpu.h
parent3e99675af1b25a191c467700499b1cbe5585a778 (diff)
ARM: 7587/1: implement optimized percpu variable access
Use the previously unused TPIDRPRW register to store percpu offsets. TPIDRPRW is only accessible in PL1, so it can only be used in the kernel. This replaces 2 loads with a mrc instruction for each percpu variable access. With hackbench, the performance improvement is 1.4% on Cortex-A9 (highbank). Taking an average of 30 runs of "hackbench -l 1000" yields: Before: 6.2191 After: 6.1348 Will Deacon reported similar delta on v6 with 11MPCore. The asm "memory clobber" are needed here to ensure the percpu offset gets reloaded. Testing by Will found that this would not happen in __schedule() which is a bit of a special case as preemption is disabled but the execution can move cores. Signed-off-by: Rob Herring <rob.herring@calxeda.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/include/asm/percpu.h')
-rw-r--r--arch/arm/include/asm/percpu.h45
1 files changed, 45 insertions, 0 deletions
diff --git a/arch/arm/include/asm/percpu.h b/arch/arm/include/asm/percpu.h
new file mode 100644
index 00000000000..968c0a14e0a
--- /dev/null
+++ b/arch/arm/include/asm/percpu.h
@@ -0,0 +1,45 @@
+/*
+ * Copyright 2012 Calxeda, Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef _ASM_ARM_PERCPU_H_
+#define _ASM_ARM_PERCPU_H_
+
+/*
+ * Same as asm-generic/percpu.h, except that we store the per cpu offset
+ * in the TPIDRPRW. TPIDRPRW only exists on V6K and V7
+ */
+#if defined(CONFIG_SMP) && !defined(CONFIG_CPU_V6)
+static inline void set_my_cpu_offset(unsigned long off)
+{
+ /* Set TPIDRPRW */
+ asm volatile("mcr p15, 0, %0, c13, c0, 4" : : "r" (off) : "memory");
+}
+
+static inline unsigned long __my_cpu_offset(void)
+{
+ unsigned long off;
+ /* Read TPIDRPRW */
+ asm("mrc p15, 0, %0, c13, c0, 4" : "=r" (off) : : "memory");
+ return off;
+}
+#define __my_cpu_offset __my_cpu_offset()
+#else
+#define set_my_cpu_offset(x) do {} while(0)
+
+#endif /* CONFIG_SMP */
+
+#include <asm-generic/percpu.h>
+
+#endif /* _ASM_ARM_PERCPU_H_ */