Good point. I’ll change it to a 32 bit uint later today.
Removing the tick based conversion removes the ability to provide the interval in various units, doesn’t it?

On 28 Jun 2021, at 17.27, Eric Dumazet [off-list ref] wrote:



quoted

On 6/28/21 2:08 PM, Niclas Hedam wrote:
This commit implements packet bursting in the NetEm scheduler.
This allows system administrators to hold back outgoing
packets and release them at a multiple of a time quantum.
This feature can be used to prevent timing attacks caused
by network latency.

Signed-off-by: Niclas Hedam <redacted>
---
v2: add enum at end of list (Cong Wang)
v3: fixed formatting of commit diff (Toke Høiland-Jørgensen)
include/uapi/linux/pkt_sched.h |  2 ++
net/sched/sch_netem.c          | 24 +++++++++++++++++++++---
2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 79a699f106b1..1ba49f141dae 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h

@@ -603,6 +603,7 @@ enum {
   TCA_NETEM_JITTER64,
   TCA_NETEM_SLOT,
   TCA_NETEM_SLOT_DIST,
+        TCA_NETEM_BURSTING,
   __TCA_NETEM_MAX,

};

@@ -615,6 +616,7 @@ struct tc_netem_qopt {
   __u32    gap;        /* re-ordering gap (0 for none) */
   __u32   duplicate;    /* random packet dup  (0=none ~0=100%) */
   __u32    jitter;        /* random jitter in latency (us) */
+    __u32    bursting;    /* send packets in bursts (us) */

};

struct tc_netem_corr {

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 0c345e43a09a..52d796287b86 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c

@@ -85,6 +85,7 @@ struct netem_sched_data {
   s64 latency;
   s64 jitter;

+    u32 bursting;
   u32 loss;
   u32 ecn;
   u32 limit;

@@ -467,7 +468,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
   /* If a delay is expected, orphan the skb. (orphaning usually takes
    * place at TX completion time, so _before_ the link transit delay)
    */
-    if (q->latency || q->jitter || q->rate)
+    if (q->latency || q->jitter || q->rate || q->bursting)
       skb_orphan_partial(skb);

   /*

@@ -527,8 +528,17 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
   qdisc_qstats_backlog_inc(sch, skb);

   cb = netem_skb_cb(skb);
-    if (q->gap == 0 ||        /* not doing reordering */
-        q->counter < q->gap - 1 ||    /* inside last reordering gap */
+    if (q->bursting > 0) {
+        u64 now;
+
+        now = ktime_get_ns();
+
+        cb->time_to_send = now - (now % q->bursting) + q->bursting;

This wont compile on 32bit arches.

quoted

+
+        ++q->counter;
+        tfifo_enqueue(skb, sch);
+    } else if (q->gap == 0 ||        /* not doing reordering */
+        q->counter < q->gap - 1 ||        /* inside last reordering gap */
       q->reorder < get_crandom(&q->reorder_cor)) {
       u64 now;
       s64 delay;

@@ -927,6 +937,7 @@ static const struct nla_policy netem_policy[TCA_NETEM_MAX + 1] = {
   [TCA_NETEM_ECN]        = { .type = NLA_U32 },
   [TCA_NETEM_RATE64]    = { .type = NLA_U64 },
   [TCA_NETEM_LATENCY64]    = { .type = NLA_S64 },
+    [TCA_NETEM_BURSTING]    = { .type = NLA_U64 },
   [TCA_NETEM_JITTER64]    = { .type = NLA_S64 },
   [TCA_NETEM_SLOT]    = { .len = sizeof(struct tc_netem_slot) },

};

@@ -1001,6 +1012,7 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,

   q->latency = PSCHED_TICKS2NS(qopt->latency);
   q->jitter = PSCHED_TICKS2NS(qopt->jitter);
+    q->bursting = PSCHED_TICKS2NS(qopt->bursting);

This is a bit silly to use 64bit user<>kernel interface
but still use the old legacy PSCHED_TICKS2NS conversion,
since this will force a big granularity.

If someone want 10 usec bursts, we should allow it.

I would simply use a 32bit value, in ns unit.

(bursts of more than 2^32 ns make no sense)

quoted

   q->limit = qopt->limit;
   q->gap = qopt->gap;
   q->counter = 0;

@@ -1032,6 +1044,9 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
   if (tb[TCA_NETEM_LATENCY64])
       q->latency = nla_get_s64(tb[TCA_NETEM_LATENCY64]);

+    if (tb[TCA_NETEM_BURSTING])
+        q->bursting = nla_get_u64(tb[TCA_NETEM_BURSTING]);
+
   if (tb[TCA_NETEM_JITTER64])
       q->jitter = nla_get_s64(tb[TCA_NETEM_JITTER64]);

@@ -1150,6 +1165,9 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff *skb)
                UINT_MAX);
   qopt.jitter = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->jitter),
               UINT_MAX);
+    qopt.bursting = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->bursting),
+                UINT_MAX);
+
   qopt.limit = q->limit;
   qopt.loss = q->loss;
   qopt.gap = q->gap;
--

2.25.1