Commit 3cad70bc authored by François Michel's avatar François Michel Committed by Jakub Kicinski
Browse files

netem: use seeded PRNG for correlated loss events 



Use prandom_u32_state() instead of get_random_u32() to generate
the correlated loss events of netem.

Signed-off-by: default avatarFrançois Michel <francois.michel@uclouvain.be>
Reviewed-by: default avatarSimon Horman <horms@kernel.org>
Acked-by: default avatarStephen Hemminger <stephen@networkplumber.org>
Link: https://lore.kernel.org/r/20230815092348.1449179-4-francois.michel@uclouvain.be


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 9c87b2ae

net/sched/sch_netem.c

+12 −10
Original line number Diff line number Diff line
@@ -184,15 +184,16 @@ static void init_crandom(struct crndstate *state, unsigned long rho) 
 * Next number depends on last value.

 * rho is scaled to avoid floating point.

 */

static u32 get_crandom(struct crndstate *state)

static u32 get_crandom(struct crndstate *state, struct prng *p)

{

	u64 value, rho;

	unsigned long answer;

	struct rnd_state *s = &p->prng_state;



	if (!state || state->rho == 0)	/* no correlation */

		return get_random_u32();

		return prandom_u32_state(s);



	value = get_random_u32();

	value = prandom_u32_state(s);

	rho = (u64)state->rho + 1;

	answer = (value * ((1ull<<32) - rho) + state->last * rho) >> 32;

	state->last = answer;
@@ -295,7 +296,7 @@ static bool loss_event(struct netem_sched_data *q) 
	switch (q->loss_model) {

	case CLG_RANDOM:

		/* Random packet drop 0 => none, ~0 => all */

		return q->loss && q->loss >= get_crandom(&q->loss_cor);

		return q->loss && q->loss >= get_crandom(&q->loss_cor, &q->prng);



	case CLG_4_STATES:

		/* 4state loss model algorithm (used also for GI model)
@@ -324,6 +325,7 @@ static bool loss_event(struct netem_sched_data *q) 
 */

static s64 tabledist(s64 mu, s32 sigma,

		     struct crndstate *state,

		     struct prng *prng,

		     const struct disttable *dist)

{

	s64 x;
@@ -333,7 +335,7 @@ static s64 tabledist(s64 mu, s32 sigma, 
	if (sigma == 0)

		return mu;



	rnd = get_crandom(state);

	rnd = get_crandom(state, prng);



	/* default uniform distribution */

	if (dist == NULL)
@@ -455,7 +457,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch, 
	skb->prev = NULL;



	/* Random duplication */

	if (q->duplicate && q->duplicate >= get_crandom(&q->dup_cor))

	if (q->duplicate && q->duplicate >= get_crandom(&q->dup_cor, &q->prng))

		++count;



	/* Drop packet? */
@@ -498,7 +500,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch, 
	 * If packet is going to be hardware checksummed, then

	 * do it now in software before we mangle it.

	 */

	if (q->corrupt && q->corrupt >= get_crandom(&q->corrupt_cor)) {

	if (q->corrupt && q->corrupt >= get_crandom(&q->corrupt_cor, &q->prng)) {

		if (skb_is_gso(skb)) {

			skb = netem_segment(skb, sch, to_free);

			if (!skb)
@@ -536,12 +538,12 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch, 
	cb = netem_skb_cb(skb);

	if (q->gap == 0 ||		/* not doing reordering */

	    q->counter < q->gap - 1 ||	/* inside last reordering gap */

	    q->reorder < get_crandom(&q->reorder_cor)) {

	    q->reorder < get_crandom(&q->reorder_cor, &q->prng)) {

		u64 now;

		s64 delay;



		delay = tabledist(q->latency, q->jitter,

				  &q->delay_cor, q->delay_dist);

				  &q->delay_cor, &q->prng, q->delay_dist);



		now = ktime_get_ns();
@@ -645,7 +647,7 @@ static void get_slot_next(struct netem_sched_data *q, u64 now) 
	else

		next_delay = tabledist(q->slot_config.dist_delay,

				       (s32)(q->slot_config.dist_jitter),

				       NULL, q->slot_dist);

				       NULL, &q->prng, q->slot_dist);



	q->slot.slot_next = now + next_delay;

	q->slot.packets_left = q->slot_config.max_packets;