From mboxrd@z Thu Jan 1 00:00:00 1970 From: robherring2@gmail.com (Rob Herring) Date: Sat, 10 Nov 2012 21:20:40 -0600 Subject: [PATCH] ARM: implement optimized percpu variable access Message-ID: <1352604040-10014-1-git-send-email-robherring2@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org From: Rob Herring 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 saves 2 loads for each percpu variable access which should yield improved performance, but the improvement has not been quantified. Signed-off-by: Rob Herring --- arch/arm/include/asm/Kbuild | 1 - arch/arm/include/asm/percpu.h | 44 +++++++++++++++++++++++++++++++++++++++++ arch/arm/kernel/smp.c | 3 +++ 3 files changed, 47 insertions(+), 1 deletion(-) create mode 100644 arch/arm/include/asm/percpu.h diff --git a/arch/arm/include/asm/Kbuild b/arch/arm/include/asm/Kbuild index f70ae17..2ffdaac 100644 --- a/arch/arm/include/asm/Kbuild +++ b/arch/arm/include/asm/Kbuild @@ -16,7 +16,6 @@ generic-y += local64.h generic-y += msgbuf.h generic-y += param.h generic-y += parport.h -generic-y += percpu.h generic-y += poll.h generic-y += resource.h generic-y += sections.h diff --git a/arch/arm/include/asm/percpu.h b/arch/arm/include/asm/percpu.h new file mode 100644 index 0000000..9eb7372 --- /dev/null +++ b/arch/arm/include/asm/percpu.h @@ -0,0 +1,44 @@ +/* + * 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 . + */ +#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. + */ +#if defined(CONFIG_SMP) && (__LINUX_ARM_ARCH__ >= 6) + +static inline void set_my_cpu_offset(unsigned long off) +{ + asm volatile("mcr p15, 0, %0, c13, c0, 4 @ set TPIDRPRW" : : "r" (off) : "cc" ); +} + +static inline unsigned long __my_cpu_offset(void) +{ + unsigned long off; + asm("mrc p15, 0, %0, c13, c0, 4 @ get TPIDRPRW" : "=r" (off) : ); + return off; +} +#define __my_cpu_offset __my_cpu_offset() +#else +#define set_my_cpu_offset(x) do {} while(0) + +#endif /* CONFIG_SMP */ + +#include + +#endif /* _ASM_ARM_PERCPU_H_ */ diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index fbc8b26..897ef60 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -313,6 +313,8 @@ asmlinkage void __cpuinit secondary_start_kernel(void) current->active_mm = mm; cpumask_set_cpu(cpu, mm_cpumask(mm)); + set_my_cpu_offset(per_cpu_offset(cpu)); + printk("CPU%u: Booted secondary processor\n", cpu); cpu_init(); @@ -371,6 +373,7 @@ void __init smp_cpus_done(unsigned int max_cpus) void __init smp_prepare_boot_cpu(void) { + set_my_cpu_offset(per_cpu_offset(smp_processor_id())); } void __init smp_prepare_cpus(unsigned int max_cpus) -- 1.7.10.4