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random: speed up the fast_mix function by a factor of four 

By mixing the entropy in chunks of 32-bit words instead of byte by
byte, we can speed up the fast_mix function significantly.  Since it
is called on every single interrupt, on systems with a very heavy
interrupt load, this can make a noticeable difference.

Also fix a compilation warning in add_interrupt_randomness() and avoid
xor'ing cycles and jiffies together just in case we have an
architecture which tries to define random_get_entropy() by returning
jiffies.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reported-by: Jörn Engel <joern@logfs.org>
This commit is contained in:
Theodore Ts'o 2013-09-22 15:24:02 -04:00
parent f5c2742c23
commit 655b226470
1 changed files with 27 additions and 21 deletions
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48
drivers/char/random.c
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@ -584,21 +584,26 @@ 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, const void *in, int nbytes)
static void fast_mix(struct fast_pool *f, __u32 input[4])
{
const char *bytes = in;
__u32 w;
unsigned i = f->count;
unsigned input_rotate = f->rotate;
while (nbytes--) {
w = rol32(*bytes++, input_rotate & 31) ^ f->pool[i & 3] ^
f->pool[(i + 1) & 3];
f->pool[i & 3] = (w >> 3) ^ twist_table[w & 7];
input_rotate += (i++ & 3) ? 7 : 14;
}
f->count = i;
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;
f->count++;
}
/*
@ -828,20 +833,21 @@ void add_interrupt_randomness(int irq, int irq_flags)
struct fast_pool *fast_pool = &__get_cpu_var(irq_randomness);
struct pt_regs *regs = get_irq_regs();
unsigned long now = jiffies;
__u32 input[4], cycles = random_get_entropy();
cycles_t cycles = random_get_entropy();
__u32 input[4], c_high, j_high;
__u64 ip;
input[0] = cycles ^ jiffies;
input[1] = irq;
if (regs) {
__u64 ip = instruction_pointer(regs);
input[2] = ip;
input[3] = ip >> 32;
}
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;
ip = regs ? instruction_pointer(regs) : _RET_IP_;
input[2] = ip;
input[3] = ip >> 32;
fast_mix(fast_pool, input, sizeof(input));
fast_mix(fast_pool, input);
if ((fast_pool->count & 1023) &&
!time_after(now, fast_pool->last + HZ))
if ((fast_pool->count & 63) && !time_after(now, fast_pool->last + HZ))
return;
fast_pool->last = now;