81880d603d
When looking at a performance problem on PowerPC, I noticed some awful code
generation:
c00000000051fc98: 3b 60 00 01 li r27,1
...
c00000000051fca0: 3b 80 00 00 li r28,0
...
c00000000051fcdc: 93 61 00 70 stw r27,112(r1)
c00000000051fce0: 93 81 00 74 stw r28,116(r1)
c00000000051fce4: 81 21 00 70 lwz r9,112(r1)
c00000000051fce8: 80 01 00 74 lwz r0,116(r1)
c00000000051fcec: 7d 29 07 b4 extsw r9,r9
c00000000051fcf0: 7c 00 07 b4 extsw r0,r0
c00000000051fcf4: 7c 20 04 ac lwsync
c00000000051fcf8: 7d 60 f8 28 lwarx r11,0,r31
c00000000051fcfc: 7c 0b 48 00 cmpw r11,r9
c00000000051fd00: 40 c2 00 10 bne- c00000000051fd10
c00000000051fd04: 7c 00 f9 2d stwcx. r0,0,r31
c00000000051fd08: 40 c2 ff f0 bne+ c00000000051fcf8
c00000000051fd0c: 4c 00 01 2c isync
We create two constants, write them out to the stack, read them straight back
in and sign extend them. What a mess.
It turns out this bad code is a result of us defining atomic_t as a
volatile int.
We removed the volatile attribute from the powerpc atomic_t definition years
ago, but commit ea43546750 (atomic_t: unify all
arch definitions) added it back in.
To dig up an old quote from Linus:
> The fact is, volatile on data structures is a bug. It's a wart in the C
> language. It shouldn't be used.
>
> Volatile accesses in *code* can be ok, and if we have "atomic_read()"
> expand to a "*(volatile int *)&(x)->value", then I'd be ok with that.
>
> But marking data structures volatile just makes the compiler screw up
> totally, and makes code for initialization sequences etc much worse.
And screw up it does :)
With the volatile removed, we see much more reasonable code generation:
c00000000051f5b8: 3b 60 00 01 li r27,1
...
c00000000051f5c0: 3b 80 00 00 li r28,0
...
c00000000051fc7c: 7c 20 04 ac lwsync
c00000000051fc80: 7c 00 f8 28 lwarx r0,0,r31
c00000000051fc84: 7c 00 d8 00 cmpw r0,r27
c00000000051fc88: 40 c2 00 10 bne- c00000000051fc98
c00000000051fc8c: 7f 80 f9 2d stwcx. r28,0,r31
c00000000051fc90: 40 c2 ff f0 bne+ c00000000051fc80
c00000000051fc94: 4c 00 01 2c isync
Six instructions less.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
209 lines
4.2 KiB
C
209 lines
4.2 KiB
C
#ifndef _LINUX_TYPES_H
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#define _LINUX_TYPES_H
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#include <asm/types.h>
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#ifndef __ASSEMBLY__
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#ifdef __KERNEL__
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#define DECLARE_BITMAP(name,bits) \
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unsigned long name[BITS_TO_LONGS(bits)]
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#endif
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#include <linux/posix_types.h>
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#ifdef __KERNEL__
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typedef __u32 __kernel_dev_t;
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typedef __kernel_fd_set fd_set;
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typedef __kernel_dev_t dev_t;
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typedef __kernel_ino_t ino_t;
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typedef __kernel_mode_t mode_t;
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typedef __kernel_nlink_t nlink_t;
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typedef __kernel_off_t off_t;
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typedef __kernel_pid_t pid_t;
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typedef __kernel_daddr_t daddr_t;
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typedef __kernel_key_t key_t;
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typedef __kernel_suseconds_t suseconds_t;
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typedef __kernel_timer_t timer_t;
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typedef __kernel_clockid_t clockid_t;
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typedef __kernel_mqd_t mqd_t;
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typedef _Bool bool;
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typedef __kernel_uid32_t uid_t;
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typedef __kernel_gid32_t gid_t;
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typedef __kernel_uid16_t uid16_t;
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typedef __kernel_gid16_t gid16_t;
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typedef unsigned long uintptr_t;
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#ifdef CONFIG_UID16
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/* This is defined by include/asm-{arch}/posix_types.h */
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typedef __kernel_old_uid_t old_uid_t;
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typedef __kernel_old_gid_t old_gid_t;
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#endif /* CONFIG_UID16 */
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#if defined(__GNUC__)
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typedef __kernel_loff_t loff_t;
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#endif
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/*
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* The following typedefs are also protected by individual ifdefs for
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* historical reasons:
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*/
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#ifndef _SIZE_T
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#define _SIZE_T
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typedef __kernel_size_t size_t;
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#endif
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#ifndef _SSIZE_T
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#define _SSIZE_T
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typedef __kernel_ssize_t ssize_t;
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#endif
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#ifndef _PTRDIFF_T
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#define _PTRDIFF_T
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typedef __kernel_ptrdiff_t ptrdiff_t;
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#endif
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#ifndef _TIME_T
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#define _TIME_T
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typedef __kernel_time_t time_t;
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#endif
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#ifndef _CLOCK_T
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#define _CLOCK_T
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typedef __kernel_clock_t clock_t;
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#endif
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#ifndef _CADDR_T
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#define _CADDR_T
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typedef __kernel_caddr_t caddr_t;
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#endif
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/* bsd */
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typedef unsigned char u_char;
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typedef unsigned short u_short;
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typedef unsigned int u_int;
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typedef unsigned long u_long;
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/* sysv */
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typedef unsigned char unchar;
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typedef unsigned short ushort;
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typedef unsigned int uint;
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typedef unsigned long ulong;
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#ifndef __BIT_TYPES_DEFINED__
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#define __BIT_TYPES_DEFINED__
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typedef __u8 u_int8_t;
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typedef __s8 int8_t;
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typedef __u16 u_int16_t;
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typedef __s16 int16_t;
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typedef __u32 u_int32_t;
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typedef __s32 int32_t;
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#endif /* !(__BIT_TYPES_DEFINED__) */
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typedef __u8 uint8_t;
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typedef __u16 uint16_t;
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typedef __u32 uint32_t;
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#if defined(__GNUC__)
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typedef __u64 uint64_t;
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typedef __u64 u_int64_t;
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typedef __s64 int64_t;
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#endif
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/* this is a special 64bit data type that is 8-byte aligned */
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#define aligned_u64 __u64 __attribute__((aligned(8)))
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#define aligned_be64 __be64 __attribute__((aligned(8)))
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#define aligned_le64 __le64 __attribute__((aligned(8)))
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/**
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* The type used for indexing onto a disc or disc partition.
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*
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* Linux always considers sectors to be 512 bytes long independently
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* of the devices real block size.
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*
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* blkcnt_t is the type of the inode's block count.
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*/
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#ifdef CONFIG_LBDAF
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typedef u64 sector_t;
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typedef u64 blkcnt_t;
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#else
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typedef unsigned long sector_t;
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typedef unsigned long blkcnt_t;
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#endif
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/*
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* The type of an index into the pagecache. Use a #define so asm/types.h
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* can override it.
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*/
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#ifndef pgoff_t
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#define pgoff_t unsigned long
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#endif
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#endif /* __KERNEL__ */
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/*
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* Below are truly Linux-specific types that should never collide with
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* any application/library that wants linux/types.h.
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*/
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#ifdef __CHECKER__
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#define __bitwise__ __attribute__((bitwise))
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#else
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#define __bitwise__
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#endif
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#ifdef __CHECK_ENDIAN__
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#define __bitwise __bitwise__
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#else
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#define __bitwise
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#endif
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typedef __u16 __bitwise __le16;
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typedef __u16 __bitwise __be16;
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typedef __u32 __bitwise __le32;
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typedef __u32 __bitwise __be32;
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typedef __u64 __bitwise __le64;
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typedef __u64 __bitwise __be64;
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typedef __u16 __bitwise __sum16;
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typedef __u32 __bitwise __wsum;
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#ifdef __KERNEL__
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typedef unsigned __bitwise__ gfp_t;
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typedef unsigned __bitwise__ fmode_t;
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#ifdef CONFIG_PHYS_ADDR_T_64BIT
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typedef u64 phys_addr_t;
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#else
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typedef u32 phys_addr_t;
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#endif
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typedef phys_addr_t resource_size_t;
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typedef struct {
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int counter;
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} atomic_t;
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#ifdef CONFIG_64BIT
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typedef struct {
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long counter;
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} atomic64_t;
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#endif
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struct ustat {
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__kernel_daddr_t f_tfree;
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__kernel_ino_t f_tinode;
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char f_fname[6];
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char f_fpack[6];
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};
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#endif /* __KERNEL__ */
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#endif /* __ASSEMBLY__ */
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#endif /* _LINUX_TYPES_H */
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