[rfc-patch 7/9] Immediate Values - Powerpc Optimization

Mathieu Desnoyers
2007-11-16T20:08:48Z

[-- Attachment #1: immediate-values-powerpc-optimization.patch --]
[-- Type: text/plain, Size: 7530 bytes --]

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.
- Pack the __immediate section. Use smallest types required for size (char).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Christoph Hellwig <hch@infradead.org>
CC: Paul Mackerras <paulus@samba.org>
---
arch/powerpc/Kconfig | 1
arch/powerpc/kernel/Makefile | 1
arch/powerpc/kernel/immediate.c | 103 ++++++++++++++++++++++++++++++++++++++++
include/asm-powerpc/immediate.h | 73 ++++++++++++++++++++++++++++
4 files changed, 178 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 2007-11-16 11:08:17.000000000 -0500
@@ -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@polymtl.ca>
+ *
+ * This file is released under the GPLv2.
+ * See the file COPYING for more details.
+ */
+
+#include <asm/asm-compat.h>
+
+struct __immediate {
+ unsigned long var; /* Identifier variable of the immediate value */
+ unsigned long immediate;/*
+ * Pointer to the memory location that holds
+ * the immediate value within the load immediate
+ * instruction.
+ */
+ unsigned char size; /* Type size. */
+} __attribute__ ((packed));
+
+/**
+ * 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 "%c1, ((0f)+3)\n\t" \
+ ".byte 1\n\t" \
+ ".previous\n\t" \
+ "0:\n\t" \
+ "li %0,0\n\t" \
+ : "=r" (value) \
+ : "i" (&name##__immediate)); \
+ break; \
+ case 2: \
+ asm(".section __immediate,\"a\",@progbits\n\t" \
+ PPC_LONG "%c1, ((0f)+2)\n\t" \
+ ".byte 2\n\t" \
+ ".previous\n\t" \
+ ".align 2\n\t" \
+ "0:\n\t" \
+ "li %0,0\n\t" \
+ : "=r" (value) \
+ : "i" (&name##__immediate)); \
+ 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 2007-11-16 10:53:01.000000000 -0500
+++ linux-2.6-lttng/arch/powerpc/kernel/Makefile 2007-11-16 11:05:38.000000000 -0500
@@ -91,3 +91,4 @@ 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 2007-11-16 11:05:38.000000000 -0500
@@ -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,
+ (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 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);
+}
Index: linux-2.6-lttng/arch/powerpc/Kconfig
===================================================================
--- linux-2.6-lttng.orig/arch/powerpc/Kconfig 2007-11-16 10:53:01.000000000 -0500
+++ linux-2.6-lttng/arch/powerpc/Kconfig 2007-11-16 11:05:38.000000000 -0500
@@ -81,6 +81,7 @@ config PPC
default y
select HAVE_OPROFILE
select HAVE_KPROBES
+ select HAVE_IMMEDIATE

config EARLY_PRINTK
bool