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random: use an improved fast_mix() function

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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@mit.edu>
Cc: George Spelvin <linux@horizon.com>
This commit is contained in:
Theodore Ts'o 2014-06-14 21:43:13 -04:00
parent 840f95077f
commit 43759d4f42
1 changed files with 66 additions and 22 deletions
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88
drivers/char/random.c
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@ -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;
__u32 a = f->pool[0], b = f->pool[1];
__u32 c = f->pool[2], d = f->pool[3];
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;
a += b; c += d;
b = rol32(a, 6); d = rol32(c, 27);
d ^= a; b ^= c;
f->rotate = input_rotate;
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) &&
@ -1650,6 +1678,22 @@ 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 */