On Thu, Aug 26, 2021 at 9:26 AM Isabella Basso <isabellabdoamaral@xxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxx/ > > Co-developed-by: Augusto Durães Camargo <augusto.duraes33@xxxxxxxxx> > Signed-off-by: Augusto Durães Camargo <augusto.duraes33@xxxxxxxxx> > Co-developed-by: Enzo Ferreira <ferreiraenzoa@xxxxxxxxx> > Signed-off-by: Enzo Ferreira <ferreiraenzoa@xxxxxxxxx> > Signed-off-by: Isabella Basso <isabellabdoamaral@xxxxxx> > --- 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 >
