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Message-Id: <1402798797-26251-1-git-send-email-tytso@mit.edu>
Date: Sat, 14 Jun 2014 22:19:57 -0400
From: Theodore Ts'o <tytso@....edu>
To: Linux Kernel Developers List <linux-kernel@...r.kernel.org>
Cc: Theodore Ts'o <tytso@....edu>, George Spelvin <linux@...izon.com>
Subject: [PATCH] random: use an improved fast_mix() function
Use more efficient fast_mix() function. Thanks to George Spelvin for
doing the leg work to find a more efficient mixing function.
Signed-off-by: Theodore Ts'o <tytso@....edu>
Cc: George Spelvin <linux@...izon.com>
---
drivers/char/random.c | 92 +++++++++++++++++++++++++++++++++++++--------------
1 file changed, 68 insertions(+), 24 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 7ff6dd4..b19edad 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -267,6 +267,8 @@
#define CREATE_TRACE_POINTS
#include <trace/events/random.h>
+/* #define ADD_INTERRUPT_BENCH */
+
/*
* Configuration information
*/
@@ -558,25 +560,29 @@ struct fast_pool {
* collector. It's hardcoded for an 128 bit pool and assumes that any
* locks that might be needed are taken by the caller.
*/
-static void fast_mix(struct fast_pool *f, __u32 input[4])
+static void fast_mix(struct fast_pool *f)
{
- __u32 w;
- unsigned input_rotate = f->rotate;
-
- w = rol32(input[0], input_rotate) ^ f->pool[0] ^ f->pool[3];
- f->pool[0] = (w >> 3) ^ twist_table[w & 7];
- input_rotate = (input_rotate + 14) & 31;
- w = rol32(input[1], input_rotate) ^ f->pool[1] ^ f->pool[0];
- f->pool[1] = (w >> 3) ^ twist_table[w & 7];
- input_rotate = (input_rotate + 7) & 31;
- w = rol32(input[2], input_rotate) ^ f->pool[2] ^ f->pool[1];
- f->pool[2] = (w >> 3) ^ twist_table[w & 7];
- input_rotate = (input_rotate + 7) & 31;
- w = rol32(input[3], input_rotate) ^ f->pool[3] ^ f->pool[2];
- f->pool[3] = (w >> 3) ^ twist_table[w & 7];
- input_rotate = (input_rotate + 7) & 31;
-
- f->rotate = input_rotate;
+ __u32 a = f->pool[0], b = f->pool[1];
+ __u32 c = f->pool[2], d = f->pool[3];
+
+ a += b; c += d;
+ b = rol32(a, 6); d = rol32(c, 27);
+ d ^= a; b ^= c;
+
+ a += b; c += d;
+ b = rol32(a, 16); d = rol32(c, 14);
+ d ^= a; b ^= c;
+
+ a += b; c += d;
+ b = rol32(a, 6); d = rol32(c, 27);
+ d ^= a; b ^= c;
+
+ a += b; c += d;
+ b = rol32(a, 16); d = rol32(c, 14);
+ d ^= a; b ^= c;
+
+ f->pool[0] = a; f->pool[1] = b;
+ f->pool[2] = c; f->pool[3] = d;
f->count++;
}
@@ -829,6 +835,27 @@ EXPORT_SYMBOL_GPL(add_input_randomness);
static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
+#ifdef ADD_INTERRUPT_BENCH
+static unsigned long avg_cycles, avg_deviation;
+
+#define AVG_SHIFT 8 /* Exponential average factor k=1/256 */
+#define FIXED_1_2 (1 << (AVG_SHIFT-1))
+
+static void add_interrupt_bench(cycles_t start)
+{
+ long delta = random_get_entropy() - start;
+
+ /* Use a weighted moving average */
+ delta = delta - ((avg_cycles + FIXED_1_2) >> AVG_SHIFT);
+ avg_cycles += delta;
+ /* And average deviation */
+ delta = abs(delta) - ((avg_deviation + FIXED_1_2) >> AVG_SHIFT);
+ avg_deviation += delta;
+}
+#else
+#define add_interrupt_bench(x)
+#endif
+
void add_interrupt_randomness(int irq, int irq_flags)
{
struct entropy_store *r;
@@ -836,22 +863,23 @@ void add_interrupt_randomness(int irq, int irq_flags)
struct pt_regs *regs = get_irq_regs();
unsigned long now = jiffies;
cycles_t cycles = random_get_entropy();
- __u32 input[4], c_high, j_high;
+ __u32 c_high, j_high;
__u64 ip;
unsigned long seed;
int credit = 0;
c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0;
j_high = (sizeof(now) > 4) ? now >> 32 : 0;
- input[0] = cycles ^ j_high ^ irq;
- input[1] = now ^ c_high;
+ fast_pool->pool[0] ^= cycles ^ j_high ^ irq;
+ fast_pool->pool[1] ^= now ^ c_high;
ip = regs ? instruction_pointer(regs) : _RET_IP_;
- input[2] = ip;
- input[3] = ip >> 32;
+ fast_pool->pool[2] ^= ip;
+ fast_pool->pool[3] ^= ip >> 32;
- fast_mix(fast_pool, input);
+ fast_mix(fast_pool);
if ((irq_flags & __IRQF_TIMER) == 0)
fast_pool->notimer_count++;
+ add_interrupt_bench(cycles);
if (cycles) {
if ((fast_pool->count < 64) &&
@@ -1648,6 +1676,22 @@ struct ctl_table random_table[] = {
.mode = 0444,
.proc_handler = proc_do_uuid,
},
+#ifdef ADD_INTERRUPT_BENCH
+ {
+ .procname = "add_interrupt_avg_cycles",
+ .data = &avg_cycles,
+ .maxlen = sizeof(avg_cycles),
+ .mode = 0444,
+ .proc_handler = proc_doulongvec_minmax,
+ },
+ {
+ .procname = "add_interrupt_avg_deviation",
+ .data = &avg_deviation,
+ .maxlen = sizeof(avg_deviation),
+ .mode = 0444,
+ .proc_handler = proc_doulongvec_minmax,
+ },
+#endif
{ }
};
#endif /* CONFIG_SYSCTL */
--
2.0.0
--
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