vfs: use 'unsigned long' accesses for dcache name comparison and hashing
Ok, this is hacky, and only works on little-endian machines with goo
unaligned handling. And even then only with CONFIG_DEBUG_PAGEALLOC
disabled, since it can access up to 7 bytes after the pathname.
But it runs like a bat out of hell.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5bed94e1..09675d3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -82,6 +82,7 @@
select CLKEVT_I8253
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select GENERIC_IOMAP
+ select DCACHE_WORD_ACCESS if !DEBUG_PAGEALLOC
config INSTRUCTION_DECODER
def_bool (KPROBES || PERF_EVENTS)
diff --git a/fs/Kconfig b/fs/Kconfig
index d621f02..aa19526 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -4,6 +4,10 @@
menu "File systems"
+# Use unaligned word dcache accesses
+config DCACHE_WORD_ACCESS
+ bool
+
if BLOCK
source "fs/ext2/Kconfig"
diff --git a/fs/dcache.c b/fs/dcache.c
index bcbdb33..ffd47a1 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -144,6 +144,28 @@
static inline int dentry_cmp(const unsigned char *cs, size_t scount,
const unsigned char *ct, size_t tcount)
{
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+ unsigned long a,b,mask;
+
+ if (unlikely(scount != tcount))
+ return 1;
+
+ for (;;) {
+ a = *(unsigned long *)cs;
+ b = *(unsigned long *)ct;
+ if (tcount < sizeof(unsigned long))
+ break;
+ if (unlikely(a != b))
+ return 1;
+ cs += sizeof(unsigned long);
+ ct += sizeof(unsigned long);
+ tcount -= sizeof(unsigned long);
+ if (!tcount)
+ return 0;
+ }
+ mask = ~(~0ul << tcount*8);
+ return unlikely(!!((a ^ b) & mask));
+#else
if (scount != tcount)
return 1;
@@ -155,6 +177,7 @@
tcount--;
} while (tcount);
return 0;
+#endif
}
static void __d_free(struct rcu_head *head)
diff --git a/fs/namei.c b/fs/namei.c
index e2ba628..378497a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1374,6 +1374,126 @@
return 1;
}
+/*
+ * We can do the critical dentry name comparison and hashing
+ * operations one word at a time, but we are limited to:
+ *
+ * - Architectures with fast unaligned word accesses. We could
+ * do a "get_unaligned()" if this helps and is sufficiently
+ * fast.
+ *
+ * - Little-endian machines (so that we can generate the mask
+ * of low bytes efficiently). Again, we *could* do a byte
+ * swapping load on big-endian architectures if that is not
+ * expensive enough to make the optimization worthless.
+ *
+ * - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we
+ * do not trap on the (extremely unlikely) case of a page
+ * crossing operation.
+ *
+ * - Furthermore, we need an efficient 64-bit compile for the
+ * 64-bit case in order to generate the "number of bytes in
+ * the final mask". Again, that could be replaced with a
+ * efficient population count instruction or similar.
+ */
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+
+#ifdef CONFIG_64BIT
+
+/*
+ * Jan Achrenius on G+: microoptimized version of
+ * the simpler "(mask & ONEBYTES) * ONEBYTES >> 56"
+ * that works for the bytemasks without having to
+ * mask them first.
+ */
+static inline long count_masked_bytes(unsigned long mask)
+{
+ return mask*0x0001020304050608 >> 56;
+}
+
+static inline unsigned int fold_hash(unsigned long hash)
+{
+ hash += hash >> (8*sizeof(int));
+ return hash;
+}
+
+#else /* 32-bit case */
+
+/* Carl Chatfield / Jan Achrenius G+ version for 32-bit */
+static inline long count_masked_bytes(long mask)
+{
+ /* (000000 0000ff 00ffff ffffff) -> ( 1 1 2 3 ) */
+ long a = (0x0ff0001+mask) >> 23;
+ /* Fix the 1 for 00 case */
+ return a & mask;
+}
+
+#define fold_hash(x) (x)
+
+#endif
+
+unsigned int full_name_hash(const unsigned char *name, unsigned int len)
+{
+ unsigned long a, mask;
+ unsigned long hash = 0;
+
+ for (;;) {
+ a = *(unsigned long *)name;
+ hash *= 9;
+ if (len < sizeof(unsigned long))
+ break;
+ hash += a;
+ name += sizeof(unsigned long);
+ len -= sizeof(unsigned long);
+ if (!len)
+ goto done;
+ }
+ mask = ~(~0ul << len*8);
+ hash += mask & a;
+done:
+ return fold_hash(hash);
+}
+EXPORT_SYMBOL(full_name_hash);
+
+#define ONEBYTES 0x0101010101010101ul
+#define SLASHBYTES 0x2f2f2f2f2f2f2f2ful
+#define HIGHBITS 0x8080808080808080ul
+
+/* Return the high bit set in the first byte that is a zero */
+static inline unsigned long has_zero(unsigned long a)
+{
+ return ((a - ONEBYTES) & ~a) & HIGHBITS;
+}
+
+/*
+ * Calculate the length and hash of the path component, and
+ * return the length of the component;
+ */
+static inline unsigned long hash_name(const char *name, unsigned int *hashp)
+{
+ unsigned long a, mask, hash, len;
+
+ hash = a = 0;
+ len = -sizeof(unsigned long);
+ do {
+ hash = (hash + a) * 9;
+ len += sizeof(unsigned long);
+ a = *(unsigned long *)(name+len);
+ /* Do we have any NUL or '/' bytes in this word? */
+ mask = has_zero(a) | has_zero(a ^ SLASHBYTES);
+ } while (!mask);
+
+ /* The mask *below* the first high bit set */
+ mask = (mask - 1) & ~mask;
+ mask >>= 7;
+ hash += a & mask;
+ *hashp = fold_hash(hash);
+
+ return len + count_masked_bytes(mask);
+}
+
+#else
+
unsigned int full_name_hash(const unsigned char *name, unsigned int len)
{
unsigned long hash = init_name_hash();
@@ -1402,6 +1522,8 @@
return len;
}
+#endif
+
/*
* Name resolution.
* This is the basic name resolution function, turning a pathname into