diff options
| author | George Spelvin <linux@sciencehorizons.net> | 2016-06-07 19:45:06 -0400 |
|---|---|---|
| committer | Helge Deller <deller@gmx.de> | 2016-08-02 16:44:29 +0200 |
| commit | 773e1c5fa4bf1faa25e119490b26ece2ef1bdb46 (patch) | |
| tree | de6e0806522d4fe791a09a0e532b51f02288227d /arch/parisc/Kconfig | |
| parent | 523d939ef98fd712632d93a5a2b588e477a7565e (diff) | |
parisc: Add <asm/hash.h>
PA-RISC is interesting; integer multiplies are implemented in the
FPU, so are painful in the kernel. But it tries to be friendly to
shift-and-add sequences for constant multiplies.
__hash_32 is implemented using the same shift-and-add sequence as
Microblaze, just scheduled for the PA7100. (It's 2-way superscalar
but in-order, like the Pentium.)
hash_64 was tricky, but a suggestion from Jason Thong allowed a
good solution by breaking up the multiplier. After a lot of manual
optimization, I found a 19-instruction sequence for the multiply that
can be executed in 10 cycles using only 4 temporaries.
(The PA8xxx can issue 4 instructions per cycle, but 2 must be ALU ops
and 2 must be loads/stores. And the final add can't be paired.)
An alternative considered, but ultimately not used, was Thomas Wang's
64-to-32-bit integer hash. At 12 instructions, it's smaller, but they're
all sequentially dependent, so it has longer latency.
https://web.archive.org/web/2011/http://www.concentric.net/~Ttwang/tech/inthash.htm
http://burtleburtle.net/bob/hash/integer.html
Signed-off-by: George Spelvin <linux@sciencehorizons.net>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-parisc@vger.kernel.org
Signed-off-by: Helge Deller <deller@gmx.de>
Diffstat (limited to 'arch/parisc/Kconfig')
| -rw-r--r-- | arch/parisc/Kconfig | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig index dc117385ce2e..cd8778103165 100644 --- a/arch/parisc/Kconfig +++ b/arch/parisc/Kconfig @@ -31,6 +31,7 @@ config PARISC select TTY # Needed for pdc_cons.c select HAVE_DEBUG_STACKOVERFLOW select HAVE_ARCH_AUDITSYSCALL + select HAVE_ARCH_HASH select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_TRACEHOOK select HAVE_UNSTABLE_SCHED_CLOCK if (SMP || !64BIT) |