Commit 43759d4f authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

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: default avatarTheodore Ts'o <tytso@mit.edu>
Cc: George Spelvin <linux@horizon.com>
parent 840f9507

drivers/char/random.c

+68 −24
Original line number Diff line number Diff line
@@ -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) &&
@@ -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 */