linux-kernel - [PATCH 09 of 12] random: remove some prefetch logic

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Message-Id: <bc31fa097d34c5c2470b.1200623631@cinder.waste.org>
Date:	Thu, 17 Jan 2008 20:33:51 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 09 of 12] 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: Matt Mackall <mpm@...enic.com>

diff -r f06a2e1b4d58 -r bc31fa097d34 drivers/char/random.c
--- a/drivers/char/random.c	Thu Jan 17 20:25:23 2008 -0600
+++ b/drivers/char/random.c	Thu Jan 17 20:25:23 2008 -0600
@@ -457,7 +457,7 @@
 	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 @@
 	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 */
--
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