On Thu, Aug 26, 2021 at 9:26 AM Isabella Basso isabellabdoamaral@usp.br wrote:
The HAVE_ARCH_HASH_32 (single underscore) define hasn't been used for any known supported architectures that have their own hash function implementation (i.e. m68k, Microblaze, H8/300, pa-risc) since George's patch [1], which introduced it.
The supported 32-bit architectures from the list above have only been making use of the (more general) HAVE_ARCH__HASH_32 define, which only lacks the right shift operator, that wasn't targeted for optimizations so far.
[1] https://lore.kernel.org/lkml/20160525073311.5600.qmail@ns.sciencehorizons.ne...
Co-developed-by: Augusto Durães Camargo augusto.duraes33@gmail.com Signed-off-by: Augusto Durães Camargo augusto.duraes33@gmail.com Co-developed-by: Enzo Ferreira ferreiraenzoa@gmail.com Signed-off-by: Enzo Ferreira ferreiraenzoa@gmail.com Signed-off-by: Isabella Basso isabellabdoamaral@usp.br
I'm not familiar with the hash functions here, so take this with the appropriate heap of salt, but it took me a little while to understand exactly what this is doing.
As I understand it: - There are separate __hash_32() and hash_32() functions. - Both of these have generic implementations, which can optionally be overridden by an architecture-specific optimised version. - There aren't any architectures which provide an optimised hash_32() implementation. - This patch therefore removes support for architecture-specific hash_32() implementations, and leaves only the generic implementation. - This generic implementation of hash_32() itself relies on __hash_32(), which may still be optimised.
Could the commit description be updated to make this a bit clearer? While we are getting rid of the HAVE_ARCH_HASH_32 #define, that seems to be a side-effect/implementation detail of removing support for architecture-specific hash_32() implementations...
The other wild, out-there option would be to remove __hash_32() entirely and make everything use hash_32(), which then could have architecture-specific implementations. A quick grep reveals that there's only one use of __hash_32() outside of the hashing code itself (in fs/namei.c). This would be much more consistent with what hash_64() does, but also would be significantly more work, and potentially could have some implication (full_name_hash() performance maybe?) which I'm not aware of. So it's possibly not worth it.
Cheers, -- David
include/linux/hash.h | 5 +---- lib/test_hash.c | 24 +----------------------- tools/include/linux/hash.h | 5 +---- 3 files changed, 3 insertions(+), 31 deletions(-)
diff --git a/include/linux/hash.h b/include/linux/hash.h index ad6fa21d977b..38edaa08f862 100644 --- a/include/linux/hash.h +++ b/include/linux/hash.h @@ -62,10 +62,7 @@ static inline u32 __hash_32_generic(u32 val) return val * GOLDEN_RATIO_32; }
-#ifndef HAVE_ARCH_HASH_32 -#define hash_32 hash_32_generic -#endif -static inline u32 hash_32_generic(u32 val, unsigned int bits) +static inline u32 hash_32(u32 val, unsigned int bits) { /* High bits are more random, so use them. */ return __hash_32(val) >> (32 - bits); diff --git a/lib/test_hash.c b/lib/test_hash.c index 0ee40b4a56dd..d4b0cfdb0377 100644 --- a/lib/test_hash.c +++ b/lib/test_hash.c @@ -94,22 +94,7 @@ test_int_hash(unsigned long long h64, u32 hash_or[2][33]) pr_err("hash_32(%#x, %d) = %#x > %#x", h0, k, h1, m); return false; } -#ifdef HAVE_ARCH_HASH_32
h2 = hash_32_generic(h0, k);
-#if HAVE_ARCH_HASH_32 == 1
if (h1 != h2) {
pr_err("hash_32(%#x, %d) = %#x != hash_32_generic() "
" = %#x", h0, k, h1, h2);
return false;
}
-#else
if (h2 > m) {
pr_err("hash_32_generic(%#x, %d) = %#x > %#x",
h0, k, h1, m);
return false;
}
-#endif -#endif
/* Test hash_64 */ hash_or[1][k] |= h1 = hash_64(h64, k); if (h1 > m) {
@@ -227,13 +212,6 @@ test_hash_init(void) #else pr_info("__hash_32() has no arch implementation to test."); #endif -#ifdef HAVE_ARCH_HASH_32 -#if HAVE_ARCH_HASH_32 != 1
pr_info("hash_32() is arch-specific; not compared to generic.");
-#endif -#else
pr_info("hash_32() has no arch implementation to test.");
-#endif #ifdef HAVE_ARCH_HASH_64 #if HAVE_ARCH_HASH_64 != 1 pr_info("hash_64() is arch-specific; not compared to generic."); diff --git a/tools/include/linux/hash.h b/tools/include/linux/hash.h index ad6fa21d977b..38edaa08f862 100644 --- a/tools/include/linux/hash.h +++ b/tools/include/linux/hash.h @@ -62,10 +62,7 @@ static inline u32 __hash_32_generic(u32 val) return val * GOLDEN_RATIO_32; }
-#ifndef HAVE_ARCH_HASH_32 -#define hash_32 hash_32_generic -#endif -static inline u32 hash_32_generic(u32 val, unsigned int bits) +static inline u32 hash_32(u32 val, unsigned int bits) { /* High bits are more random, so use them. */ return __hash_32(val) >> (32 - bits); -- 2.33.0