From 7a0268fa1a3613f2c526a9b3058701b277f6abe1 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Wed, 11 Jan 2006 13:16:44 +1100 Subject: [PATCH] [PATCH] powerpc/64: per cpu data optimisations The current ppc64 per cpu data implementation is quite slow. eg: lhz 11,18(13) /* smp_processor_id() */ ld 9,.LC63-.LCTOC1(30) /* per_cpu__variable_name */ ld 8,.LC61-.LCTOC1(30) /* __per_cpu_offset */ sldi 11,11,3 /* form index into __per_cpu_offset */ mr 10,9 ldx 9,11,8 /* __per_cpu_offset[smp_processor_id()] */ ldx 0,10,9 /* load per cpu data */ 5 loads for something that is supposed to be fast, pretty awful. One reason for the large number of loads is that we have to synthesize 2 64bit constants (per_cpu__variable_name and __per_cpu_offset). By putting __per_cpu_offset into the paca we can avoid the 2 loads associated with it: ld 11,56(13) /* paca->data_offset */ ld 9,.LC59-.LCTOC1(30) /* per_cpu__variable_name */ ldx 0,9,11 /* load per cpu data Longer term we can should be able to do even better than 3 loads. If per_cpu__variable_name wasnt a 64bit constant and paca->data_offset was in a register we could cut it down to one load. A suggestion from Rusty is to use gcc's __thread extension here. In order to do this we would need to free up r13 (the __thread register and where the paca currently is). So far Ive had a few unsuccessful attempts at doing that :) The patch also allocates per cpu memory node local on NUMA machines. This patch from Rusty has been sitting in my queue _forever_ but stalled when I hit the compiler bug. Sorry about that. Finally I also only allocate per cpu data for possible cpus, which comes straight out of the x86-64 port. On a pseries kernel (with NR_CPUS == 128) and 4 possible cpus we see some nice gains: total used free shared buffers cached Mem: 4012228 212860 3799368 0 0 162424 total used free shared buffers cached Mem: 4016200 212984 3803216 0 0 162424 A saving of 3.75MB. Quite nice for smaller machines. Note: we now have to be careful of per cpu users that touch data for !possible cpus. At this stage it might be worth making the NUMA and possible cpu optimisations generic, but per cpu init is done so early we have to be careful that all architectures have their possible map setup correctly. Signed-off-by: Anton Blanchard Signed-off-by: Paul Mackerras --- arch/powerpc/kernel/setup_64.c | 26 ++++++++++++++++ include/asm-powerpc/paca.h | 1 + include/asm-powerpc/percpu.h | 56 ++++++++++++++++++++++++++++++++++ 3 files changed, 83 insertions(+) diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c index 0420418f317a..e29b275e09e0 100644 --- a/arch/powerpc/kernel/setup_64.c +++ b/arch/powerpc/kernel/setup_64.c @@ -33,6 +33,7 @@ #include #include #include +#include #include #include #include @@ -654,3 +655,28 @@ void cpu_die(void) if (ppc_md.cpu_die) ppc_md.cpu_die(); } + +#ifdef CONFIG_SMP +void __init setup_per_cpu_areas(void) +{ + int i; + unsigned long size; + char *ptr; + + /* Copy section for each CPU (we discard the original) */ + size = ALIGN(__per_cpu_end - __per_cpu_start, SMP_CACHE_BYTES); +#ifdef CONFIG_MODULES + if (size < PERCPU_ENOUGH_ROOM) + size = PERCPU_ENOUGH_ROOM; +#endif + + for_each_cpu(i) { + ptr = alloc_bootmem_node(NODE_DATA(cpu_to_node(i)), size); + if (!ptr) + panic("Cannot allocate cpu data for CPU %d\n", i); + + paca[i].data_offset = ptr - __per_cpu_start; + memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start); + } +} +#endif diff --git a/include/asm-powerpc/paca.h b/include/asm-powerpc/paca.h index 3ae52d9dc9ff..a64b4d425dab 100644 --- a/include/asm-powerpc/paca.h +++ b/include/asm-powerpc/paca.h @@ -65,6 +65,7 @@ struct paca_struct { u64 stab_real; /* Absolute address of segment table */ u64 stab_addr; /* Virtual address of segment table */ void *emergency_sp; /* pointer to emergency stack */ + u64 data_offset; /* per cpu data offset */ s16 hw_cpu_id; /* Physical processor number */ u8 cpu_start; /* At startup, processor spins until */ /* this becomes non-zero. */ diff --git a/include/asm-powerpc/percpu.h b/include/asm-powerpc/percpu.h index 06a959d67234..e31922c50e53 100644 --- a/include/asm-powerpc/percpu.h +++ b/include/asm-powerpc/percpu.h @@ -1 +1,57 @@ +#ifndef _ASM_POWERPC_PERCPU_H_ +#define _ASM_POWERPC_PERCPU_H_ +#ifdef __powerpc64__ +#include + +/* + * Same as asm-generic/percpu.h, except that we store the per cpu offset + * in the paca. Based on the x86-64 implementation. + */ + +#ifdef CONFIG_SMP + +#include + +#define __per_cpu_offset(cpu) (paca[cpu].data_offset) +#define __my_cpu_offset() get_paca()->data_offset + +/* Separate out the type, so (int[3], foo) works. */ +#define DEFINE_PER_CPU(type, name) \ + __attribute__((__section__(".data.percpu"))) __typeof__(type) per_cpu__##name + +/* var is in discarded region: offset to particular copy we want */ +#define per_cpu(var, cpu) (*RELOC_HIDE(&per_cpu__##var, __per_cpu_offset(cpu))) +#define __get_cpu_var(var) (*RELOC_HIDE(&per_cpu__##var, __my_cpu_offset())) + +/* A macro to avoid #include hell... */ +#define percpu_modcopy(pcpudst, src, size) \ +do { \ + unsigned int __i; \ + for (__i = 0; __i < NR_CPUS; __i++) \ + if (cpu_possible(__i)) \ + memcpy((pcpudst)+__per_cpu_offset(__i), \ + (src), (size)); \ +} while (0) + +extern void setup_per_cpu_areas(void); + +#else /* ! SMP */ + +#define DEFINE_PER_CPU(type, name) \ + __typeof__(type) per_cpu__##name + +#define per_cpu(var, cpu) (*((void)(cpu), &per_cpu__##var)) +#define __get_cpu_var(var) per_cpu__##var + +#endif /* SMP */ + +#define DECLARE_PER_CPU(type, name) extern __typeof__(type) per_cpu__##name + +#define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(per_cpu__##var) +#define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(per_cpu__##var) + +#else #include +#endif + +#endif /* _ASM_POWERPC_PERCPU_H_ */ -- 2.30.2