random: remove some prefetch logic

The urandom output pool (ie the fast path) fits in one cacheline, so
this is pretty unnecessary. Further, the output path has already
fetched the entire pool to hash it before calling in here.

(This was the only user of prefetch_range in the kernel, and it passed
in words rather than bytes!)
Signed-off-by: NMatt Mackall <mpm@selenic.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/char/random.c

@@ -457,7 +457,7 @@ static void __add_entropy_words(struct entropy_store *r, const __u32 *in,
 	unsigned long i, add_ptr, tap1, tap2, tap3, tap4, tap5;
 	int input_rotate;
 	int wordmask = r->poolinfo->poolwords - 1;
-	__u32 w, next_w;
+	__u32 w;
 	unsigned long flags;
 
 	/* Taps are constant, so we can load them without holding r->lock.  */
@@ -466,17 +466,13 @@ static void __add_entropy_words(struct entropy_store *r, const __u32 *in,
 	tap3 = r->poolinfo->tap3;
 	tap4 = r->poolinfo->tap4;
 	tap5 = r->poolinfo->tap5;
-	next_w = *in++;
 
 	spin_lock_irqsave(&r->lock, flags);
-	prefetch_range(r->pool, wordmask);
 	input_rotate = r->input_rotate;
 	add_ptr = r->add_ptr;
 
 	while (nwords--) {
-		w = rol32(next_w, input_rotate & 31);
-		if (nwords > 0)
-			next_w = *in++;
+		w = rol32(*in++, input_rotate & 31);
 		i = add_ptr = (add_ptr - 1) & wordmask;
 
 		/* XOR in the various taps */