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Merge branch 'reusable-codel'
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Michal Kazior says:

====================
codel: make it reuseable beyond qdiscs

There's an ongoing effort in fixing wireless
bufferbloat. As part of that fq_codel is being
ported into mac80211. To prevent code duplication
codel.h needs to be slightly modified before it
can be used in mac80211 (or other drivers FWIW).

For more background please see:

  https://www.spinics.net/lists/linux-wireless/msg149976.html
====================

Signed-off-by: David S. Miller <davem@davemloft.net>
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David S. Miller committed Apr 25, 2016
2 parents e425974 + d068ca2 commit 05d82c4
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Showing 5 changed files with 368 additions and 220 deletions.
217 changes: 4 additions & 213 deletions include/net/codel.h
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Original file line number Diff line number Diff line change
Expand Up @@ -87,27 +87,6 @@ static inline codel_time_t codel_get_time(void)
((s32)((a) - (b)) >= 0))
#define codel_time_before_eq(a, b) codel_time_after_eq(b, a)

/* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
struct codel_skb_cb {
codel_time_t enqueue_time;
};

static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
{
qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb));
return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data;
}

static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
{
return get_codel_cb(skb)->enqueue_time;
}

static void codel_set_enqueue_time(struct sk_buff *skb)
{
get_codel_cb(skb)->enqueue_time = codel_get_time();
}

static inline u32 codel_time_to_us(codel_time_t val)
{
u64 valns = ((u64)val << CODEL_SHIFT);
Expand Down Expand Up @@ -176,198 +155,10 @@ struct codel_stats {

#define CODEL_DISABLED_THRESHOLD INT_MAX

static void codel_params_init(struct codel_params *params,
const struct Qdisc *sch)
{
params->interval = MS2TIME(100);
params->target = MS2TIME(5);
params->mtu = psched_mtu(qdisc_dev(sch));
params->ce_threshold = CODEL_DISABLED_THRESHOLD;
params->ecn = false;
}

static void codel_vars_init(struct codel_vars *vars)
{
memset(vars, 0, sizeof(*vars));
}

static void codel_stats_init(struct codel_stats *stats)
{
stats->maxpacket = 0;
}

/*
* http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
* new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
*
* Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
*/
static void codel_Newton_step(struct codel_vars *vars)
{
u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);

val >>= 2; /* avoid overflow in following multiply */
val = (val * invsqrt) >> (32 - 2 + 1);

vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
}

/*
* CoDel control_law is t + interval/sqrt(count)
* We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
* both sqrt() and divide operation.
*/
static codel_time_t codel_control_law(codel_time_t t,
codel_time_t interval,
u32 rec_inv_sqrt)
{
return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
}

static bool codel_should_drop(const struct sk_buff *skb,
struct Qdisc *sch,
struct codel_vars *vars,
struct codel_params *params,
struct codel_stats *stats,
codel_time_t now)
{
bool ok_to_drop;

if (!skb) {
vars->first_above_time = 0;
return false;
}

vars->ldelay = now - codel_get_enqueue_time(skb);
sch->qstats.backlog -= qdisc_pkt_len(skb);

if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket))
stats->maxpacket = qdisc_pkt_len(skb);

if (codel_time_before(vars->ldelay, params->target) ||
sch->qstats.backlog <= params->mtu) {
/* went below - stay below for at least interval */
vars->first_above_time = 0;
return false;
}
ok_to_drop = false;
if (vars->first_above_time == 0) {
/* just went above from below. If we stay above
* for at least interval we'll say it's ok to drop
*/
vars->first_above_time = now + params->interval;
} else if (codel_time_after(now, vars->first_above_time)) {
ok_to_drop = true;
}
return ok_to_drop;
}

typedef u32 (*codel_skb_len_t)(const struct sk_buff *skb);
typedef codel_time_t (*codel_skb_time_t)(const struct sk_buff *skb);
typedef void (*codel_skb_drop_t)(struct sk_buff *skb, void *ctx);
typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
struct Qdisc *sch);
void *ctx);

static struct sk_buff *codel_dequeue(struct Qdisc *sch,
struct codel_params *params,
struct codel_vars *vars,
struct codel_stats *stats,
codel_skb_dequeue_t dequeue_func)
{
struct sk_buff *skb = dequeue_func(vars, sch);
codel_time_t now;
bool drop;

if (!skb) {
vars->dropping = false;
return skb;
}
now = codel_get_time();
drop = codel_should_drop(skb, sch, vars, params, stats, now);
if (vars->dropping) {
if (!drop) {
/* sojourn time below target - leave dropping state */
vars->dropping = false;
} else if (codel_time_after_eq(now, vars->drop_next)) {
/* It's time for the next drop. Drop the current
* packet and dequeue the next. The dequeue might
* take us out of dropping state.
* If not, schedule the next drop.
* A large backlog might result in drop rates so high
* that the next drop should happen now,
* hence the while loop.
*/
while (vars->dropping &&
codel_time_after_eq(now, vars->drop_next)) {
vars->count++; /* dont care of possible wrap
* since there is no more divide
*/
codel_Newton_step(vars);
if (params->ecn && INET_ECN_set_ce(skb)) {
stats->ecn_mark++;
vars->drop_next =
codel_control_law(vars->drop_next,
params->interval,
vars->rec_inv_sqrt);
goto end;
}
stats->drop_len += qdisc_pkt_len(skb);
qdisc_drop(skb, sch);
stats->drop_count++;
skb = dequeue_func(vars, sch);
if (!codel_should_drop(skb, sch,
vars, params, stats, now)) {
/* leave dropping state */
vars->dropping = false;
} else {
/* and schedule the next drop */
vars->drop_next =
codel_control_law(vars->drop_next,
params->interval,
vars->rec_inv_sqrt);
}
}
}
} else if (drop) {
u32 delta;

if (params->ecn && INET_ECN_set_ce(skb)) {
stats->ecn_mark++;
} else {
stats->drop_len += qdisc_pkt_len(skb);
qdisc_drop(skb, sch);
stats->drop_count++;

skb = dequeue_func(vars, sch);
drop = codel_should_drop(skb, sch, vars, params,
stats, now);
}
vars->dropping = true;
/* if min went above target close to when we last went below it
* assume that the drop rate that controlled the queue on the
* last cycle is a good starting point to control it now.
*/
delta = vars->count - vars->lastcount;
if (delta > 1 &&
codel_time_before(now - vars->drop_next,
16 * params->interval)) {
vars->count = delta;
/* we dont care if rec_inv_sqrt approximation
* is not very precise :
* Next Newton steps will correct it quadratically.
*/
codel_Newton_step(vars);
} else {
vars->count = 1;
vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
}
vars->lastcount = vars->count;
vars->drop_next = codel_control_law(now, params->interval,
vars->rec_inv_sqrt);
}
end:
if (skb && codel_time_after(vars->ldelay, params->ce_threshold) &&
INET_ECN_set_ce(skb))
stats->ce_mark++;
return skb;
}
#endif
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