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fd476197c6
task's arch specific bits are carried in 2 places - embedded thread_struct in task_struct - associated thread_info (hoisted in task's stack page) and syntactically: (thread_info *)(task_struct->stack) ksp (dynamic kernel stack top) currently lives in thread_struct but given its deep location in task struct likely to cache miss when accessed from __switch_to(). Moving it to thread_info would be more efficient given proximity to frequently accessed items such as preempt_count thus very likely to be in cache, specially in schedular code. Note however that currently tsk.thread.ksp takes 1 memory access (off of tsk pointer) while new code tsk->stack.ksp would take 2, but likely to be in cache. Moreover if task is current the 2nd reference can be elided and instead derived from SP as (SP & ~(THREAD_SIZE - 1)) All of this also makes __switch_to() code simpler and we can see the 2 ways of retirving ksp (descrobed above) in new code. Signed-off-by: Vineet Gupta <vgupta@kernel.org>
64 lines
1.4 KiB
ArmAsm
64 lines
1.4 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
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*
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* Vineetg: Aug 2009
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* -Moved core context switch macro out of entry.S into this file.
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* -This is the more "natural" hand written assembler
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*/
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#include <linux/linkage.h>
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#include <asm/entry.h> /* For the SAVE_* macros */
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#include <asm/asm-offsets.h>
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; IN
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; - r0: prev task (also current)
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; - r1: next task
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; OUT
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; - r0: prev task (so r0 not touched)
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.section .sched.text,"ax",@progbits
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ENTRY_CFI(__switch_to)
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/* save kernel stack frame regs of @prev task */
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push blink
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CFI_DEF_CFA_OFFSET 4
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CFI_OFFSET r31, -4
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push fp
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CFI_DEF_CFA_OFFSET 8
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CFI_OFFSET r27, -8
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mov fp, sp
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CFI_DEF_CFA_REGISTER r27
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/* kernel mode callee regs of @prev */
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SAVE_CALLEE_SAVED_KERNEL
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/*
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* save final SP to @prev->thread_info.ksp
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* @prev is "current" so thread_info derived from SP
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*/
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GET_CURR_THR_INFO_FROM_SP r10
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st sp, [r10, THREAD_INFO_KSP]
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/* update @next in _current_task[] and GP register caching it */
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SET_CURR_TASK_ON_CPU r1, r10
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/* load SP from @next->thread_info.ksp */
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ld r10, [r1, TASK_THREAD_INFO]
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ld sp, [r10, THREAD_INFO_KSP]
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/* restore callee regs, stack frame regs of @next */
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RESTORE_CALLEE_SAVED_KERNEL
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pop fp
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CFI_RESTORE r27
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CFI_DEF_CFA r28, 4
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pop blink
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CFI_RESTORE r31
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CFI_DEF_CFA_OFFSET 0
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j [blink]
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END_CFI(__switch_to)
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