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MIPS: Align swapper_pg_dir to 64K for better TLB Refill code.

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We can save an instruction in the TLB Refill path for kernel mappings
by aligning swapper_pg_dir on a 64K boundary.  The address of
swapper_pg_dir can be generated with a single LUI instead of
LUI/{D}ADDUI.

The alignment of __init_end is bumped up to 64K so there are no holes
between it and swapper_pg_dir, which is placed at the very beginning
of .bss.

The alignment of invalid_pmd_table and invalid_pte_table can be
relaxed to PAGE_SIZE.  We do this by using __page_aligned_bss, which
has the added benefit of eliminating alignment holes in .bss.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-arch@vger.kernel.org,
Cc: linux-kernel@vger.kernel.org
Acked-by: Arnd Bergmann <arnd@arndb.de>
Patchwork: https://patchwork.linux-mips.org/patch/4220/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
David Daney 2012-08-14 11:08:01 -07:00 committed by Ralf Baechle
parent c87728ca82
commit 485172b3df
2 changed files with 28 additions and 10 deletions
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21
arch/mips/kernel/vmlinux.lds.S
View File

@ -1,6 +1,13 @@
#include <asm/asm-offsets.h>
#include <asm/page.h>
#include <asm/thread_info.h>
/*
* Put .bss..swapper_pg_dir as the first thing in .bss. This will
* ensure that it has .bss alignment (64K).
*/
#define BSS_FIRST_SECTIONS *(.bss..swapper_pg_dir)
#include <asm-generic/vmlinux.lds.h>
#undef mips
@ -119,11 +126,21 @@ SECTIONS
}
PERCPU_SECTION(1 << CONFIG_MIPS_L1_CACHE_SHIFT)
. = ALIGN(PAGE_SIZE);
/*
* Align to 64K in attempt to eliminate holes before the
* .bss..swapper_pg_dir section at the start of .bss. This
* also satisfies PAGE_SIZE alignment as the largest page size
* allowed is 64K.
*/
. = ALIGN(0x10000);
__init_end = .;
/* freed after init ends here */
BSS_SECTION(0, 0, 0)
/*
* Force .bss to 64K alignment so that .bss..swapper_pg_dir
* gets that alignment. .sbss should be empty, so there will be
* no holes after __init_end. */
BSS_SECTION(0, 0x10000, 0)
_end = . ;

17
arch/mips/mm/init.c
View File

@ -469,19 +469,20 @@ void __init_refok free_initmem(void)
#ifndef CONFIG_MIPS_PGD_C0_CONTEXT
unsigned long pgd_current[NR_CPUS];
#endif
/*
* On 64-bit we've got three-level pagetables with a slightly
* different layout ...
*/
#define __page_aligned(order) __attribute__((__aligned__(PAGE_SIZE<<order)))
/*
* gcc 3.3 and older have trouble determining that PTRS_PER_PGD and PGD_ORDER
* are constants. So we use the variants from asm-offset.h until that gcc
* will officially be retired.
*
* Align swapper_pg_dir in to 64K, allows its address to be loaded
* with a single LUI instruction in the TLB handlers. If we used
* __aligned(64K), its size would get rounded up to the alignment
* size, and waste space. So we place it in its own section and align
* it in the linker script.
*/
pgd_t swapper_pg_dir[_PTRS_PER_PGD] __page_aligned(_PGD_ORDER);
pgd_t swapper_pg_dir[_PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
#ifndef __PAGETABLE_PMD_FOLDED
pmd_t invalid_pmd_table[PTRS_PER_PMD] __page_aligned(PMD_ORDER);
pmd_t invalid_pmd_table[PTRS_PER_PMD] __page_aligned_bss;
#endif
pte_t invalid_pte_table[PTRS_PER_PTE] __page_aligned(PTE_ORDER);
pte_t invalid_pte_table[PTRS_PER_PTE] __page_aligned_bss;