[patch 5/7] Immediate Values - Powerpc Optimization
From: Mathieu Desnoyers
Date: Tue Sep 18 2007 - 17:11:01 EST
PowerPC optimization of the immediate values which uses a li instruction,
patched with an immediate value.
Changelog:
- Put immediate_set and _immediate_set in the architecture independent header.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
CC: Christoph Hellwig <hch@xxxxxxxxxxxxx>
---
arch/powerpc/kernel/Makefile | 1
arch/powerpc/kernel/immediate.c | 103 ++++++++++++++++++++++++++++++++++++++++
include/asm-powerpc/immediate.h | 73 ++++++++++++++++++++++++++++
3 files changed, 177 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 2007-09-17 13:39:02.000000000 -0400
@@ -0,0 +1,73 @@
+#ifndef _ASM_POWERPC_IMMEDIATE_H
+#define _ASM_POWERPC_IMMEDIATE_H
+
+/*
+ * Immediate values. PowerPC architecture optimizations.
+ *
+ * (C) Copyright 2006 Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
+ *
+ * This file is released under the GPLv2.
+ * See the file COPYING for more details.
+ */
+
+#include <asm/asm-compat.h>
+
+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
+ * @name: immediate value name
+ *
+ * Reads the value of @name.
+ * 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(name) \
+ ({ \
+ __typeof__(name##__immediate) 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" (&name##__immediate), \
+ "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" (&name##__immediate), \
+ "i" (0)); \
+ break; \
+ default: \
+ value = name##__immediate; \
+ break; \
+ }; \
+ value; \
+ })
+
+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 2007-09-17 13:37:03.000000000 -0400
+++ linux-2.6-lttng/arch/powerpc/kernel/Makefile 2007-09-17 13:38:54.000000000 -0400
@@ -97,3 +97,4 @@ 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 2007-09-17 13:38:54.000000000 -0400
@@ -0,0 +1,103 @@
+/*
+ * Powerpc optimized immediate values enabling/disabling.
+ *
+ * Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
+ */
+
+#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,
+ (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,
+ (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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