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Subject[RFC Patch v1 32/55] ARC: [optim] Cache "current" in Register r25
Date
From: Vineet Gupta <vgupta@synopsys.com>

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
arch/arc/Kconfig | 7 ++++++
arch/arc/Makefile | 9 +++++++
arch/arc/include/asm/Kbuild | 1 -
arch/arc/include/asm/current.h | 32 +++++++++++++++++++++++++++
arch/arc/include/asm/entry.h | 45 ++++++++++++++++++++++++++++++++++++++
arch/arc/include/asm/processor.h | 3 ++
arch/arc/kernel/asm-offsets.c | 3 ++
arch/arc/kernel/ctx_sw.c | 7 ++++++
arch/arc/kernel/entry.S | 14 +++++++++++
9 files changed, 120 insertions(+), 1 deletions(-)
create mode 100644 arch/arc/include/asm/current.h

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index f3aacfc..71e55c0 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -277,6 +277,13 @@ config ARC_PLAT_SDRAM_SIZE

endmenu # "Platform Board Configuration"

+config ARC_CURR_IN_REG
+ bool "Dedicate Register r25 for current_task pointer"
+ default y
+ help
+ This reserved Register R25 to point to Current Task in
+ kernel mode. This saves memory access for each such access
+
config ARC_STACK_NONEXEC
bool "Make stack non-executable"
default n
diff --git a/arch/arc/Makefile b/arch/arc/Makefile
index 4d52a3b..eeb64dd 100644
--- a/arch/arc/Makefile
+++ b/arch/arc/Makefile
@@ -20,6 +20,15 @@ export PLATFORM
cflags-y += -Iarch/arc/plat-$(PLATFORM)/include
cflags-y += -mA7 -fno-common -pipe -fno-builtin -D__linux__

+ifdef CONFIG_ARC_CURR_IN_REG
+# For a global register defintion, make sure it gets passed to every file
+# We had a customer reported bug where some code built in kernel was NOT using
+# any kernel headers, and missing the r25 global register
+# Can't do unconditionally (like above) because of recursive include issues
+# due to <linux/thread_info.h>
+LINUXINCLUDE += -include ${src}/arch/arc/include/asm/current.h
+endif
+
atleast_gcc44 := $(call cc-ifversion, -gt, 0402, y)
cflags-$(atleast_gcc44) += -fsection-anchors

diff --git a/arch/arc/include/asm/Kbuild b/arch/arc/include/asm/Kbuild
index 148dfcf..a246390 100644
--- a/arch/arc/include/asm/Kbuild
+++ b/arch/arc/include/asm/Kbuild
@@ -11,7 +11,6 @@ generic-y += bugs.h
generic-y += bitsperlong.h
generic-y += clkdev.h
generic-y += cputime.h
-generic-y += current.h
generic-y += device.h
generic-y += div64.h
generic-y += emergency-restart.h
diff --git a/arch/arc/include/asm/current.h b/arch/arc/include/asm/current.h
new file mode 100644
index 0000000..87b9185
--- /dev/null
+++ b/arch/arc/include/asm/current.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Vineetg: May 16th, 2008
+ * - Current macro is now implemented as "global register" r25
+ */
+
+#ifndef _ASM_ARC_CURRENT_H
+#define _ASM_ARC_CURRENT_H
+
+#ifdef __KERNEL__
+
+#ifndef __ASSEMBLY__
+
+#ifdef CONFIG_ARC_CURR_IN_REG
+
+register struct task_struct *curr_arc asm("r25");
+#define current (curr_arc)
+
+#else
+#include <asm-generic/current.h>
+#endif /* ! CONFIG_ARC_CURR_IN_REG */
+
+#endif /* ! __ASSEMBLY__ */
+
+#endif /* __KERNEL__ */
+
+#endif /* _ASM_ARC_CURRENT_H */
diff --git a/arch/arc/include/asm/entry.h b/arch/arc/include/asm/entry.h
index 3e0a9f4..6113e1a 100644
--- a/arch/arc/include/asm/entry.h
+++ b/arch/arc/include/asm/entry.h
@@ -13,6 +13,8 @@
* was being "CLEARED" rather then "SET". Actually "SET" clears ZOL context
*
* Vineetg: May 5th 2008
+ * -Modified CALLEE_REG save/restore macros to handle the fact that
+ * r25 contains the kernel current task ptr
* - Defined Stack Switching Macro to be reused in all intr/excp hdlrs
* - Shaved off 11 instructions from RESTORE_ALL_INT1 by using the
* address Write back load ld.ab instead of seperate ld/add instn
@@ -28,6 +30,7 @@
#include <asm/asm-offsets.h>
#include <asm/arcregs.h>
#include <asm/ptrace.h>
+#include <asm/processor.h> /* For VMALLOC_START */
#include <asm/thread_info.h> /* For THREAD_SIZE */

/* Note on the LD/ST addr modes with addr reg wback
@@ -106,7 +109,14 @@
st.a r22, [sp, -4]
st.a r23, [sp, -4]
st.a r24, [sp, -4]
+
+#ifdef CONFIG_ARC_CURR_IN_REG
+ ; Retrieve orig r25 and save it on stack
+ ld r12, [r25, TASK_THREAD + THREAD_USER_R25]
+ st.a r12, [sp, -4]
+#else
st.a r25, [sp, -4]
+#endif

/* move up by 1 word to "create" callee_regs->"stack_place_holder" */
sub sp, sp, 4
@@ -131,8 +141,12 @@
st.a r22, [sp, -4]
st.a r23, [sp, -4]
st.a r24, [sp, -4]
+#ifdef CONFIG_ARC_CURR_IN_REG
+ sub sp, sp, 8
+#else
st.a r25, [sp, -4]
sub sp, sp, 4
+#endif
.endm

/*--------------------------------------------------------------
@@ -148,8 +162,14 @@
*-------------------------------------------------------------*/
.macro RESTORE_CALLEE_SAVED_KERNEL

+
+#ifdef CONFIG_ARC_CURR_IN_REG
+ add sp, sp, 8 /* skip callee_reg gutter and user r25 placeholder */
+#else
add sp, sp, 4 /* skip "callee_regs->stack_place_holder" */
ld.ab r25, [sp, 4]
+#endif
+
ld.ab r24, [sp, 4]
ld.ab r23, [sp, 4]
ld.ab r22, [sp, 4]
@@ -200,6 +220,7 @@
*
* Entry : r9 contains pre-IRQ/exception/trap status32
* Exit : SP is set to kernel mode stack pointer
+ * If CURR_IN_REG, r25 set to "current" task pointer
* Clobbers: r9
*-------------------------------------------------------------*/

@@ -224,6 +245,16 @@

GET_CURR_TASK_ON_CPU r9

+#ifdef CONFIG_ARC_CURR_IN_REG
+
+ /* If current task pointer cached in r25, time to
+ * -safekeep USER r25 in task->thread_struct->user_r25
+ * -load r25 with current task ptr
+ */
+ st.as r25, [r9, (TASK_THREAD + THREAD_USER_R25)/4]
+ mov r25, r9
+#endif
+
/* With current tsk in r9, get it's kernel mode stack base */
GET_TSK_STACK_BASE r9, r9

@@ -479,17 +510,31 @@

.macro SET_CURR_TASK_ON_CPU tsk, tmp
st \tsk, [@_current_task]
+#ifdef CONFIG_ARC_CURR_IN_REG
+ mov r25, \tsk
+#endif
.endm

/* ------------------------------------------------------------------
* Get the ptr to some field of Current Task at @off in task struct
+ * -Uses r25 for Current task ptr if that is enabled
*/

+#ifdef CONFIG_ARC_CURR_IN_REG
+
+.macro GET_CURR_TASK_FIELD_PTR off, reg
+ add \reg, r25, \off
+.endm
+
+#else
+
.macro GET_CURR_TASK_FIELD_PTR off, reg
GET_CURR_TASK_ON_CPU \reg
add \reg, \reg, \off
.endm

+#endif /* CONFIG_ARC_CURR_IN_REG */
+
#endif /* __ASSEMBLY__ */

#endif /* __ASM_ARC_ENTRY_H */
diff --git a/arch/arc/include/asm/processor.h b/arch/arc/include/asm/processor.h
index 38ea5fb..2fe9f22 100644
--- a/arch/arc/include/asm/processor.h
+++ b/arch/arc/include/asm/processor.h
@@ -29,6 +29,9 @@ struct thread_struct {
unsigned long callee_reg; /* pointer to callee regs */
unsigned long fault_address; /* dbls as brkpt holder as well */
unsigned long cause_code; /* Exception Cause Code (ECR) */
+#ifdef CONFIG_ARC_CURR_IN_REG
+ unsigned long user_r25;
+#endif
#ifdef CONFIG_ARC_FPU_SAVE_RESTORE
struct arc_fpu fpu;
#endif
diff --git a/arch/arc/kernel/asm-offsets.c b/arch/arc/kernel/asm-offsets.c
index 7f3f611..b0e7254 100644
--- a/arch/arc/kernel/asm-offsets.c
+++ b/arch/arc/kernel/asm-offsets.c
@@ -23,6 +23,9 @@ int main(void)

DEFINE(THREAD_KSP, offsetof(struct thread_struct, ksp));
DEFINE(THREAD_CALLEE_REG, offsetof(struct thread_struct, callee_reg));
+#ifdef CONFIG_ARC_CURR_IN_REG
+ DEFINE(THREAD_USER_R25, offsetof(struct thread_struct, user_r25));
+#endif
DEFINE(THREAD_FAULT_ADDR,
offsetof(struct thread_struct, fault_address));

diff --git a/arch/arc/kernel/ctx_sw.c b/arch/arc/kernel/ctx_sw.c
index 647e37a..fbf739c 100644
--- a/arch/arc/kernel/ctx_sw.c
+++ b/arch/arc/kernel/ctx_sw.c
@@ -24,6 +24,9 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
unsigned int prev = (unsigned int)prev_task;
unsigned int next = (unsigned int)next_task;
int num_words_to_skip = 1;
+#ifdef CONFIG_ARC_CURR_IN_REG
+ num_words_to_skip++;
+#endif

__asm__ __volatile__(
/* FP/BLINK save generated by gcc (standard function prologue */
@@ -39,7 +42,9 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
"st.a r22, [sp, -4] \n\t"
"st.a r23, [sp, -4] \n\t"
"st.a r24, [sp, -4] \n\t"
+#ifndef CONFIG_ARC_CURR_IN_REG
"st.a r25, [sp, -4] \n\t"
+#endif
"sub sp, sp, %4 \n\t" /* create gutter at top */

/* set ksp of outgoing task in tsk->thread.ksp */
@@ -62,7 +67,9 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)

"add sp, sp, %4 \n\t" /* skip gutter at top */

+#ifndef CONFIG_ARC_CURR_IN_REG
"ld.ab r25, [sp, 4] \n\t"
+#endif
"ld.ab r24, [sp, 4] \n\t"
"ld.ab r23, [sp, 4] \n\t"
"ld.ab r22, [sp, 4] \n\t"
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index deb2652..35406da 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -36,6 +36,9 @@
* was being "CLEARED" rather then "SET". Since it is Loop INHIBIT Bit,
* setting it and not clearing it clears ZOL context
*
+ * Vineetg: May 16th, 2008
+ * - r25 now contains the Current Task when in kernel
+ *
* Vineetg: Dec 22, 2007
* Minor Surgery of Low Level ISR to make it SMP safe
* - MMU_SCRATCH0 Reg used for freeing up r9 in Level 1 ISR
@@ -540,6 +543,17 @@ restore_regs :
; XXX can this be optimised out
IRQ_DISABLE_SAVE r9, r10 ;@r10 has prisitine (pre-disable) copy

+#ifdef CONFIG_ARC_CURR_IN_REG
+ ; Restore User R25
+ ; Earlier this used to be only for returning to user mode
+ ; However with 2 levels of IRQ this can also happen even if
+ ; in kernel mode
+ ld r9, [sp, PT_sp]
+ brhs r9, VMALLOC_START, 8f
+ RESTORE_USER_R25
+8:
+#endif
+
; Restore REG File. In case multiple Events outstanding,
; use the same priorty as rtie: EXCPN, L2 IRQ, L1 IRQ, None
; Note that we use realtime STATUS32 (not pt_regs->status32) to
--
1.7.4.1


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