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authorLinus Torvalds <torvalds@linux-foundation.org>2016-05-28 16:15:25 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-05-28 16:15:25 -0700
commit7e0fb73c52c4037b4d5ef9ff56c7296a3151bd92 (patch)
tree9ab023505d388563d937b3c3ac26ef3c2045dba2 /arch/h8300/include
parent4e8440b3b6b801953b2e53c55491cf98fc8f6c01 (diff)
parent4684fe95300c071983f77653e354c040fe80a265 (diff)
Merge branch 'hash' of git://ftp.sciencehorizons.net/linux
Pull string hash improvements from George Spelvin: "This series does several related things: - Makes the dcache hash (fs/namei.c) useful for general kernel use. (Thanks to Bruce for noticing the zero-length corner case) - Converts the string hashes in <linux/sunrpc/svcauth.h> to use the above. - Avoids 64-bit multiplies in hash_64() on 32-bit platforms. Two 32-bit multiplies will do well enough. - Rids the world of the bad hash multipliers in hash_32. This finishes the job started in commit 689de1d6ca95 ("Minimal fix-up of bad hashing behavior of hash_64()") The vast majority of Linux architectures have hardware support for 32x32-bit multiply and so derive no benefit from "simplified" multipliers. The few processors that do not (68000, h8/300 and some models of Microblaze) have arch-specific implementations added. Those patches are last in the series. - Overhauls the dcache hash mixing. The patch in commit 0fed3ac866ea ("namei: Improve hash mixing if CONFIG_DCACHE_WORD_ACCESS") was an off-the-cuff suggestion. Replaced with a much more careful design that's simultaneously faster and better. (My own invention, as there was noting suitable in the literature I could find. Comments welcome!) - Modify the hash_name() loop to skip the initial HASH_MIX(). This would let us salt the hash if we ever wanted to. - Sort out partial_name_hash(). The hash function is declared as using a long state, even though it's truncated to 32 bits at the end and the extra internal state contributes nothing to the result. And some callers do odd things: - fs/hfs/string.c only allocates 32 bits of state - fs/hfsplus/unicode.c uses it to hash 16-bit unicode symbols not bytes - Modify bytemask_from_count to handle inputs of 1..sizeof(long) rather than 0..sizeof(long)-1. This would simplify users other than full_name_hash" Special thanks to Bruce Fields for testing and finding bugs in v1. (I learned some humbling lessons about "obviously correct" code.) On the arch-specific front, the m68k assembly has been tested in a standalone test harness, I've been in contact with the Microblaze maintainers who mostly don't care, as the hardware multiplier is never omitted in real-world applications, and I haven't heard anything from the H8/300 world" * 'hash' of git://ftp.sciencehorizons.net/linux: h8300: Add <asm/hash.h> microblaze: Add <asm/hash.h> m68k: Add <asm/hash.h> <linux/hash.h>: Add support for architecture-specific functions fs/namei.c: Improve dcache hash function Eliminate bad hash multipliers from hash_32() and hash_64() Change hash_64() return value to 32 bits <linux/sunrpc/svcauth.h>: Define hash_str() in terms of hashlen_string() fs/namei.c: Add hashlen_string() function Pull out string hash to <linux/stringhash.h>
Diffstat (limited to 'arch/h8300/include')
-rw-r--r--arch/h8300/include/asm/hash.h53
1 files changed, 53 insertions, 0 deletions
diff --git a/arch/h8300/include/asm/hash.h b/arch/h8300/include/asm/hash.h
new file mode 100644
index 000000000000..04cfbd2bd850
--- /dev/null
+++ b/arch/h8300/include/asm/hash.h
@@ -0,0 +1,53 @@
+#ifndef _ASM_HASH_H
+#define _ASM_HASH_H
+
+/*
+ * The later H8SX models have a 32x32-bit multiply, but the H8/300H
+ * and H8S have only 16x16->32. Since it's tolerably compact, this is
+ * basically an inlined version of the __mulsi3 code. Since the inputs
+ * are not expected to be small, it's also simplfied by skipping the
+ * early-out checks.
+ *
+ * (Since neither CPU has any multi-bit shift instructions, a
+ * shift-and-add version is a non-starter.)
+ *
+ * TODO: come up with an arch-specific version of the hashing in fs/namei.c,
+ * since that is heavily dependent on rotates. Which, as mentioned, suck
+ * horribly on H8.
+ */
+
+#if defined(CONFIG_CPU_H300H) || defined(CONFIG_CPU_H8S)
+
+#define HAVE_ARCH__HASH_32 1
+
+/*
+ * Multiply by k = 0x61C88647. Fitting this into three registers requires
+ * one extra instruction, but reducing register pressure will probably
+ * make that back and then some.
+ *
+ * GCC asm note: %e1 is the high half of operand %1, while %f1 is the
+ * low half. So if %1 is er4, then %e1 is e4 and %f1 is r4.
+ *
+ * This has been designed to modify x in place, since that's the most
+ * common usage, but preserve k, since hash_64() makes two calls in
+ * quick succession.
+ */
+static inline u32 __attribute_const__ __hash_32(u32 x)
+{
+ u32 temp;
+
+ asm( "mov.w %e1,%f0"
+ "\n mulxu.w %f2,%0" /* klow * xhigh */
+ "\n mov.w %f0,%e1" /* The extra instruction */
+ "\n mov.w %f1,%f0"
+ "\n mulxu.w %e2,%0" /* khigh * xlow */
+ "\n add.w %e1,%f0"
+ "\n mulxu.w %f2,%1" /* klow * xlow */
+ "\n add.w %f0,%e1"
+ : "=&r" (temp), "=r" (x)
+ : "%r" (GOLDEN_RATIO_32), "1" (x));
+ return x;
+}
+
+#endif
+#endif /* _ASM_HASH_H */