On Thu, Feb 5, 2026 at 10:13 AM Paul Moses [off-list ref] wrote:

Looks like pedit might also affected. Hopefully this makes it more clear. Going to wait on more input before doing anything else with this.

NLMSG_GOODSIZE = SKB_WITH_OVERHEAD(min(PAGE_SIZE, 8192))
SKB_WITH_OVERHEAD(X) = X - SKB_DATA_ALIGN(sizeof(struct skb_shared_info))
nla_total_size(payload) = NLA_ALIGN(NLA_HDRLEN + payload), with NLA_HDRLEN = 4 and 4 byte alignment

Per entry size for the gate list:

Each entry is a nested TCA_GATE_ONE_ENTRY plus five attributes:

TCA_GATE_ONE_ENTRY (nest, no payload) -> 4
INDEX (u32) -> 8
GATE (flag, no payload) -> 4
INTERVAL (u32) -> 8
MAX_OCTETS (s32) -> 8
IPV (s32) -> 8

So one entry is:

entry_sz = 4 + 8 + 4 + 8 + 8 + 8 = 40 bytes

Fixed overhead for one act_gate dump:

1. Action wrapper (RTM_GETACTION):

NLMSG_HDRLEN + sizeof(struct tcamsg) + nla_total_size(0)
= 16 + 4 + 4 = 24 bytes

2. Action shared attributes emitted by tcf_action_dump_1, baseline only
   (no cookie, no HW stats, no flags):

TCA_ACT_KIND (IFNAMSIZ) = 20
TCA_ACT_STATS nest = 4
TCA_STATS_BASIC = 20
TCA_STATS_PKT64 = 12
TCA_STATS_QUEUE = 24
TCA_ACT_OPTIONS nest = 4
TCA_GACT_TM = 36
TCA_ACT_IN_HW_COUNT = 8
action number nest = 4

Total shared baseline = 156 bytes

Optional shared attributes, only if present:

TCA_ACT_HW_STATS = +12
TCA_ACT_USED_HW_STATS = +12
TCA_ACT_FLAGS = +12
TCA_ACT_COOKIE = +nla_total_size(cookie_len)

3. Gate specific attributes inside options, fixed part including TM:

TCA_GATE_PARMS = 24
BASE_TIME = 12
CYCLE_TIME = 12
CYCLE_TIME_EXT = 12
CLOCKID = 8
FLAGS = 8
PRIORITY = 8
ENTRY_LIST nest = 4
TCA_GATE_TM = 36

Total gate baseline = 124 bytes

4. 64 bit alignment padding, only when
   !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS

There are 7 attributes that trigger the 64 bit padding:
-three stats blocks, three time values and the gate TM
-Each adds 4 bytes, so add 28 bytes in that case

Putting it together:

fixed = 24 (wrapper) + 156 (shared baseline) + 124 (gate baseline)
fixed = 304 bytes

opt = nla_total_size(cookie_len)
+ 12 for each of HW_STATS, USED_HW_STATS and FLAGS if present
+ 28 if unaligned access padding is required

The maximum number of entries that fit in a single skb is:

Nmax = floor((NLMSG_GOODSIZE - fixed - opt) / 40)

If PAGE_SIZE = 4096 and sizeof(struct skb_shared_info) = 320:

NLMSG_GOODSIZE = 4096 - 320 = 3776
Nmax = floor((3776 - 304) / 40) = 86

8192:

NLMSG_GOODSIZE = 8192 - 320 = 7872
Nmax = floor((7872 - 304) / 40) = 189

Seems arbitrary and I was hoping you dont have to change iproute2
which restricts the total size to 1KB.
Earlier, unless i misread, you said you are looking at IEEE - what
does the spec say?
If i am not mistaken, the spec is   IEEE 802.1Qbv which unfortunately
is behind a paywall.
The closest i could find was a vendor talking about it here:
https://onlinedocs.microchip.com/oxy/GUID-82119957-1E11-4B69-84AC-EF0EA08F5595-en-US-5/GUID-7E7509A4-351E-4D82-8266-967681BA2644.html

And they seem to indicate you can only have _one_ off and one timer
per queue, for a max of 8 queues.
Since Po is AWOL, +Cc the taprio folks (Vinicius, Vladmir).

cheers,
jamal