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author | Nicholas Piggin <npiggin@gmail.com> | 2017-01-04 04:58:28 +1000 |
---|---|---|
committer | Michael Ellerman <mpe@ellerman.id.au> | 2017-02-18 14:40:01 +1100 |
commit | d11914b21c4c21a294fe8937d66c1a192caa3cad (patch) | |
tree | c4b6822062b0d542c772979eb05ba20abbdae3f8 /arch/powerpc/include/asm/bitops.h | |
parent | 02983449c87b1dfd9b75af4c8a2a8057f9664c08 (diff) | |
download | linux-d11914b21c4c21a294fe8937d66c1a192caa3cad.tar.bz2 |
powerpc/64: Implement clear_bit_unlock_is_negative_byte()
Commit b91e1302ad9b8 ("mm: optimize PageWaiters bit use for
unlock_page()") added a special bitop function to speed up
unlock_page(). Implement this for 64-bit powerpc.
This improves the unlock_page() core code from this:
li 9,1
lwsync
1: ldarx 10,0,3,0
andc 10,10,9
stdcx. 10,0,3
bne- 1b
ori 2,2,0
ld 9,0(3)
andi. 10,9,0x80
beqlr
li 4,0
b wake_up_page_bit
To this:
li 10,1
lwsync
1: ldarx 9,0,3,0
andc 9,9,10
stdcx. 9,0,3
bne- 1b
andi. 10,9,0x80
beqlr
li 4,0
b wake_up_page_bit
In a test of elapsed time for dd writing into 16GB of already-dirty
pagecache on a POWER8 with 4K pages, which has one unlock_page per 4kB
this patch reduced overhead by 1.1%:
N Min Max Median Avg Stddev
x 19 2.578 2.619 2.594 2.595 0.011
+ 19 2.552 2.592 2.564 2.565 0.008
Difference at 95.0% confidence
-0.030 +/- 0.006
-1.142% +/- 0.243%
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Made 64-bit only until I can test it properly on 32-bit]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/include/asm/bitops.h')
-rw-r--r-- | arch/powerpc/include/asm/bitops.h | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/arch/powerpc/include/asm/bitops.h b/arch/powerpc/include/asm/bitops.h index 59abc620f8e8..73eb794d6163 100644 --- a/arch/powerpc/include/asm/bitops.h +++ b/arch/powerpc/include/asm/bitops.h @@ -154,6 +154,34 @@ static __inline__ int test_and_change_bit(unsigned long nr, return test_and_change_bits(BIT_MASK(nr), addr + BIT_WORD(nr)) != 0; } +#ifdef CONFIG_PPC64 +static __inline__ unsigned long clear_bit_unlock_return_word(int nr, + volatile unsigned long *addr) +{ + unsigned long old, t; + unsigned long *p = (unsigned long *)addr + BIT_WORD(nr); + unsigned long mask = BIT_MASK(nr); + + __asm__ __volatile__ ( + PPC_RELEASE_BARRIER +"1:" PPC_LLARX(%0,0,%3,0) "\n" + "andc %1,%0,%2\n" + PPC405_ERR77(0,%3) + PPC_STLCX "%1,0,%3\n" + "bne- 1b\n" + : "=&r" (old), "=&r" (t) + : "r" (mask), "r" (p) + : "cc", "memory"); + + return old; +} + +/* This is a special function for mm/filemap.c */ +#define clear_bit_unlock_is_negative_byte(nr, addr) \ + (clear_bit_unlock_return_word(nr, addr) & BIT_MASK(PG_waiters)) + +#endif /* CONFIG_PPC64 */ + #include <asm-generic/bitops/non-atomic.h> static __inline__ void __clear_bit_unlock(int nr, volatile unsigned long *addr) |