From f2db633d301b4b50f5f93de0e8314cc81e9bc7de Mon Sep 17 00:00:00 2001 From: Michael Cree Date: Sun, 19 Aug 2012 14:40:58 +1200 Subject: alpha: Use new generic strncpy_from_user() and strnlen_user() Similar to x86/sparc/powerpc implementations except: 1) we implement an extremely efficient has_zero()/find_zero() sequence with both prep_zero_mask() and create_zero_mask() no-operations. 2) Our output from prep_zero_mask() differs in that only the lowest eight bits are used to represent the zero bytes nevertheless it can be safely ORed with other similar masks from prep_zero_mask() and forms input to create_zero_mask(), the two fundamental properties prep_zero_mask() must satisfy. Tests on EV67 and EV68 CPUs revealed that the generic code is essentially as fast (to within 0.5% of CPU cycles) of the old Alpha specific code for large quadword-aligned strings, despite the 30% extra CPU instructions executed. In contrast, the generic code for unaligned strings is substantially slower (by more than a factor of 3) than the old Alpha specific code. Signed-off-by: Michael Cree Acked-by: Matt Turner Signed-off-by: Linus Torvalds --- arch/alpha/include/asm/word-at-a-time.h | 55 +++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) create mode 100644 arch/alpha/include/asm/word-at-a-time.h (limited to 'arch/alpha/include/asm/word-at-a-time.h') diff --git a/arch/alpha/include/asm/word-at-a-time.h b/arch/alpha/include/asm/word-at-a-time.h new file mode 100644 index 000000000000..6b340d0f1521 --- /dev/null +++ b/arch/alpha/include/asm/word-at-a-time.h @@ -0,0 +1,55 @@ +#ifndef _ASM_WORD_AT_A_TIME_H +#define _ASM_WORD_AT_A_TIME_H + +#include + +/* + * word-at-a-time interface for Alpha. + */ + +/* + * We do not use the word_at_a_time struct on Alpha, but it needs to be + * implemented to humour the generic code. + */ +struct word_at_a_time { + const unsigned long unused; +}; + +#define WORD_AT_A_TIME_CONSTANTS { 0 } + +/* Return nonzero if val has a zero */ +static inline unsigned long has_zero(unsigned long val, unsigned long *bits, const struct word_at_a_time *c) +{ + unsigned long zero_locations = __kernel_cmpbge(0, val); + *bits = zero_locations; + return zero_locations; +} + +static inline unsigned long prep_zero_mask(unsigned long val, unsigned long bits, const struct word_at_a_time *c) +{ + return bits; +} + +#define create_zero_mask(bits) (bits) + +static inline unsigned long find_zero(unsigned long bits) +{ +#if defined(CONFIG_ALPHA_EV6) && defined(CONFIG_ALPHA_EV67) + /* Simple if have CIX instructions */ + return __kernel_cttz(bits); +#else + unsigned long t1, t2, t3; + /* Retain lowest set bit only */ + bits &= -bits; + /* Binary search for lowest set bit */ + t1 = bits & 0xf0; + t2 = bits & 0xcc; + t3 = bits & 0xaa; + if (t1) t1 = 4; + if (t2) t2 = 2; + if (t3) t3 = 1; + return t1 + t2 + t3; +#endif +} + +#endif /* _ASM_WORD_AT_A_TIME_H */ -- cgit v1.2.3