Messages in this thread Patch in this message |  | | | Date | Mon, 28 Apr 2008 16:04:47 +0200 (CEST) | | From | Thomas Gleixner <> | | Subject | Re: [PATCH] bitops: simplify generic bit finding functions |
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On Sun, 27 Apr 2008, Linus Torvalds wrote: > On Sun, 27 Apr 2008, Harvey Harrison wrote: > > > > No need for a sentinal if we explicitly catch the no bits/all bits set > > cases, make it clear they are special cases returning size/BITS_PER_LONG. > > These things need to be re-done anyway. David already complained that the > thing inlines to something much much too big.
The delta between the inlined version including the constant optimizations and the original non inlined version is exactly 1400 bytes on a sparc64 defconfig build.
> Let's just make it not be an inline at all.
Which makes the whole constant optimization moot.
How about making the optimization controlled by a config switch so arch maintainers can decide whether they want to enable the constant optimization or unconditionally call the lib function ?
See patch below. It gives back the 1400 bytes on SPARC64 and other platforms that have no instruction for find bit.
Thanks, tglx
----------> Subject: bitops: optional bitops mapsize optimization on config switch From: Thomas Gleixner <tglx@linutronix.de> Date: Mon, 28 Apr 2008 00:22:06 +0200
The mapsize optimizations which were moved from x86 to the generic code in commit 64970b68d2b3ed32b964b0b30b1b98518fde388e increased the binary size on non x86 architectures.
Make the optimization depend on a config switch so architecture maintainers can decide.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Ingo Molnar <mingo@elte.hu>
--- arch/x86/Kconfig.cpu | 1 + include/linux/bitops.h | 6 ++++-- 2 files changed, 5 insertions(+), 2 deletions(-) Index: linux-2.6/arch/x86/Kconfig.cpu =================================================================== --- linux-2.6.orig/arch/x86/Kconfig.cpu +++ linux-2.6/arch/x86/Kconfig.cpu @@ -282,6 +282,7 @@ config X86_CPU def_bool y select GENERIC_FIND_FIRST_BIT select GENERIC_FIND_NEXT_BIT + select GENERIC_FIND_BIT_MAPSIZE_OPTIMIZE config X86_GENERIC bool "Generic x86 support" Index: linux-2.6/include/linux/bitops.h =================================================================== --- linux-2.6.orig/include/linux/bitops.h +++ linux-2.6/include/linux/bitops.h @@ -190,6 +190,7 @@ static __always_inline unsigned long find_next_bit(const unsigned long *addr, unsigned long size, unsigned long offset) { +#ifdef CONFIG_GENERIC_FIND_BIT_MAPSIZE_OPTIMIZE unsigned long value; /* Avoid a function call if the bitmap size is a constant */ @@ -209,7 +210,7 @@ find_next_bit(const unsigned long *addr, value = (*addr) & ((~0ul) << offset); return (value == 0) ? BITS_PER_LONG : __ffs(value); } - +#endif /* size is not constant or too big */ return __find_next_bit(addr, size, offset); } @@ -227,6 +228,7 @@ static __always_inline unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size, unsigned long offset) { +#ifdef CONFIG_GENERIC_FIND_BIT_MAPSIZE_OPTIMIZE unsigned long value; /* Avoid a function call if the bitmap size is a constant */ @@ -246,7 +248,7 @@ find_next_zero_bit(const unsigned long * value = (~(*addr)) & ((~0ul) << offset); return (value == 0) ? BITS_PER_LONG : __ffs(value); } - +#endif /* size is not constant or too big */ return __find_next_zero_bit(addr, size, offset); }
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