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    Subject[patch 6/8] Immediate Values - Powerpc Optimization
    PowerPC optimization of the immediate values which uses a li instruction,
    patched with an immediate value.

    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    CC: Christoph Hellwig <hch@infradead.org>
    ---
    arch/powerpc/kernel/Makefile | 1
    arch/powerpc/kernel/immediate.c | 103 ++++++++++++++++++++++++++++++++
    include/asm-powerpc/immediate.h | 127 ++++++++++++++++++++++++++++++++++++++++
    3 files changed, 231 insertions(+)

    Index: linux-2.6-lttng/include/asm-powerpc/immediate.h
    ===================================================================
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ linux-2.6-lttng/include/asm-powerpc/immediate.h 2007-08-07 13:33:13.000000000 -0400
    @@ -0,0 +1,127 @@
    +#ifndef _ASM_POWERPC_IMMEDIATE_H
    +#define _ASM_POWERPC_IMMEDIATE_H
    +
    +/*
    + * Immediate values. PowerPC architecture optimizations.
    + *
    + * (C) Copyright 2006 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    + *
    + * This file is released under the GPLv2.
    + * See the file COPYING for more details.
    + */
    +
    +#include <asm/asm-compat.h>
    +
    +struct module;
    +
    +struct __immediate {
    + long var; /* Identifier variable of the immediate value */
    + long immediate; /*
    + * Pointer to the memory location that holds
    + * the immediate value within the load immediate
    + * instruction.
    + */
    + long size; /* Type size. */
    +};
    +
    +/**
    + * immediate_read - read immediate variable
    + * @var: pointer of type immediate_*_t
    + *
    + * Reads the value of @var.
    + * Optimized version of the immediate.
    + * Do not use in __init and __exit functions. Use _immediate_read() instead.
    + * Makes sure the 2 bytes update will be atomic by aligning the immediate
    + * value. Use a normal memory read for the 4 bytes immediate because there is no
    + * way to atomically update it without using a seqlock read side, which would
    + * cost more in term of total i-cache and d-cache space than a simple memory
    + * read.
    + */
    +#define immediate_read(var) \
    + ({ \
    + __typeof__((var)->value) value; \
    + switch (sizeof(value)) { \
    + case 1: \
    + asm ( ".section __immediate, \"a\", @progbits;\n\t" \
    + PPC_LONG "%1, ((0f)+3), 1;\n\t" \
    + ".previous;\n\t" \
    + "0:\n\t" \
    + "li %0,%2;\n\t" \
    + : "=r" (value) \
    + : "i" (&(var)->value), \
    + "i" (0)); \
    + break; \
    + case 2: \
    + asm ( ".section __immediate, \"a\", @progbits;\n\t" \
    + PPC_LONG "%1, ((0f)+2), 2;\n\t" \
    + ".previous;\n\t" \
    + ".align 2\n\t" \
    + "0:\n\t" \
    + "li %0,%2;\n\t" \
    + : "=r" (value) \
    + : "i" (&(var)->value), \
    + "i" (0)); \
    + break; \
    + default: \
    + value = (var)->value; \
    + break; \
    + }; \
    + value; \
    + })
    +
    +/**
    + * immediate_set - set immediate variable (with locking)
    + * @var: pointer of type immediate_*_t
    + * @i: required value
    + *
    + * Sets the value of @var, taking the module_mutex if required by
    + * the architecture.
    + */
    +#define immediate_set(var, i) \
    + (var)->value = (i); \
    + immediate_update(1);
    +
    +/**
    + * _immediate_set - set immediate variable (without locking)
    + * @var: pointer of type immediate_*_t
    + * @i: required value
    + *
    + * Sets the value of @var. Must be called with module_mutex held.
    + */
    +#define _immediate_set(var, i) \
    + (var)->value = (i); \
    + immediate_update(0);
    +
    +/**
    + * immediate_set_early - set immediate variable at early boot
    + * @var: pointer of type immediate_*_t
    + * @i: required value
    + *
    + * Sets the value of @var. Should be used for early boot updates.
    + */
    +#define immediate_set_early(var, i) \
    + (var)->value = (i); \
    + immediate_update_early();
    +
    +/**
    + * immediate_if - if () statement depending on an immediate value
    + * @var: pointer of type immediate_*_t
    + *
    + * Use as an if () statement depending on an immediate value.
    + * Do not use in __init and __exit functions. Use _immediate_if() instead.
    + * Branch depending on an immediate value. Could eventually be optimized further
    + * by improving gcc to give the ability to patch a jump instruction instead of
    + * the value it depends on.
    + */
    +#define immediate_if(var) if (unlikely(immediate_read(var)))
    +
    +/*
    + * Internal update functions.
    + */
    +extern void immediate_update(int lock);
    +extern void module_immediate_setup(struct module *mod);
    +extern void immediate_update_early(void);
    +extern int arch_immediate_update(const struct __immediate *immediate);
    +extern void arch_immediate_update_early(const struct __immediate *immediate);
    +
    +#endif /* _ASM_POWERPC_IMMEDIATE_H */
    Index: linux-2.6-lttng/arch/powerpc/kernel/Makefile
    ===================================================================
    --- linux-2.6-lttng.orig/arch/powerpc/kernel/Makefile 2007-08-07 13:32:35.000000000 -0400
    +++ linux-2.6-lttng/arch/powerpc/kernel/Makefile 2007-08-07 13:32:53.000000000 -0400
    @@ -103,3 +103,4 @@ obj-$(CONFIG_PPC64) += $(obj64-y)

    extra-$(CONFIG_PPC_FPU) += fpu.o
    extra-$(CONFIG_PPC64) += entry_64.o
    +obj-$(CONFIG_IMMEDIATE) += immediate.o
    Index: linux-2.6-lttng/arch/powerpc/kernel/immediate.c
    ===================================================================
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ linux-2.6-lttng/arch/powerpc/kernel/immediate.c 2007-08-07 13:33:20.000000000 -0400
    @@ -0,0 +1,103 @@
    +/*
    + * Powerpc optimized immediate values enabling/disabling.
    + *
    + * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    + */
    +
    +#include <linux/module.h>
    +#include <linux/immediate.h>
    +#include <linux/string.h>
    +#include <linux/kprobes.h>
    +#include <asm/cacheflush.h>
    +#include <asm/page.h>
    +
    +#define LI_OPCODE_LEN 2
    +
    +/**
    + * arch_immediate_update - update one immediate value
    + * @immediate: pointer of type const struct __immediate to update
    + *
    + * Update one immediate value. Must be called with immediate_mutex held.
    + */
    +int arch_immediate_update(const struct __immediate *immediate)
    +{
    +#ifdef CONFIG_KPROBES
    + kprobe_opcode_t *insn;
    + /*
    + * Fail if a kprobe has been set on this instruction.
    + * (TODO: we could eventually do better and modify all the (possibly
    + * nested) kprobes for this site if kprobes had an API for this.
    + */
    + switch (immediate->size) {
    + case 1: /* The uint8_t points to the 3rd byte of the
    + * instruction */
    + insn = (void*)(immediate->immediate - 1 - LI_OPCODE_LEN);
    + break;
    + case 2: insn = (void*)(immediate->immediate - LI_OPCODE_LEN);
    + break;
    + default:
    + return -EINVAL;
    + }
    +
    + if (unlikely(*insn == BREAKPOINT_INSTRUCTION)) {
    + printk(KERN_WARNING "Immediate value in conflict with kprobe. "
    + "Variable at %p, "
    + "instruction at %p, size %lu\n",
    + (void*)immediate->immediate,
    + (void*)immediate->var, immediate->size);
    + return -EBUSY;
    + }
    +#endif
    +
    + /*
    + * If the variable and the instruction have the same value, there is
    + * nothing to do.
    + */
    + switch (immediate->size) {
    + case 1: if (*(uint8_t*)immediate->immediate
    + == *(uint8_t*)immediate->var)
    + return 0;
    + break;
    + case 2: if (*(uint16_t*)immediate->immediate
    + == *(uint16_t*)immediate->var)
    + return 0;
    + break;
    + default:return -EINVAL;
    + }
    + memcpy((void*)immediate->immediate, (void*)immediate->var,
    + immediate->size);
    + flush_icache_range((unsigned long)immediate->immediate,
    + immediate->size);
    + return 0;
    +}
    +
    +/**
    + * arch_immediate_update_early - update one immediate value at boot time
    + * @immediate: pointer of type const struct __immediate to update
    + *
    + * Update one immediate value at boot time.
    + * We can use flush_icache_range, since the cpu identification has been done in
    + * the early_init stage.
    + */
    +void __init arch_immediate_update_early(const struct __immediate *immediate)
    +{
    + /*
    + * If the variable and the instruction have the same value, there is
    + * nothing to do.
    + */
    + switch (immediate->size) {
    + case 1: if (*(uint8_t*)immediate->immediate
    + == *(uint8_t*)immediate->var)
    + return;
    + break;
    + case 2: if (*(uint16_t*)immediate->immediate
    + == *(uint16_t*)immediate->var)
    + return;
    + break;
    + default:return;
    + }
    + memcpy((void*)immediate->immediate, (void*)immediate->var,
    + immediate->size);
    + flush_icache_range((unsigned long)immediate->immediate,
    + immediate->size);
    +}
    --
    Mathieu Desnoyers
    Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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