From 655b226470b229552ad95b21323864df9bd9fc74 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Sun, 22 Sep 2013 15:24:02 -0400 Subject: [PATCH] random: speed up the fast_mix function by a factor of four MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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" Reported-by: Jörn Engel --- drivers/char/random.c | 50 ++++++++++++++++++++++++------------------- 1 file changed, 28 insertions(+), 22 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index a68b4a093272..74eeec58e779 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -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(); - - input[0] = cycles ^ jiffies; - input[1] = irq; - if (regs) { - __u64 ip = instruction_pointer(regs); - input[2] = ip; - input[3] = ip >> 32; - } + cycles_t cycles = random_get_entropy(); + __u32 input[4], c_high, j_high; + __u64 ip; + + 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; -- 2.39.5