On RTX 4060 Ti 16 GB + RTX 3060 12 GB (48 layers, IQ3_S) the first pick was K=2 and the #1616 retry
(every stage at least 3 layers) landed on its own edge, K=3: the 3060 ran 3 layers, 12 GB idle, 452 tok/s of
prefill against 802 at 28 layers (the prompt flows through the stages as a pipeline). For two GPUs the retry
now first asks for a placement in which each stage owns at least floor(layers x its room / all rooms) layers
(split_rules::share_floors, at least 3, trimmed to fit); the three-layer rule stays the second try and the
first pick the last, and the log says which one was taken. Nothing changes where the first pick has no
one- or two-layer stage (equal cards), and three or more GPUs keep the #1616 rule alone.
Reported by @Tworks25 on #2644, with the sweep of layer_split 12..32 (PR #2643). split_rules_test gets the
reporter's rooms (14.2 GiB and 5.50 GiB) and the identical-card and degenerate cases.
0.1.41 (0391e478) scaled each stage's miss term by 20 GB/s / its probed link, for 2x 4090 D
with CUDA1 on a physical x1 link (1.6 GB/s: x12, K 22 -> 38, prompt ~350 -> ~1400 tok/s).
On 2x Tesla T10 the same rule moved auto from K=23 to K=14: CUDA1 runs 34 of 48 layers, and as
the prompt path is a pipeline the slower stage sets the rate - 256K prompt 1035 -> 795 tok/s,
decode 46.8 -> 39.5; --layer-split 23 on 0.1.43 restores both (xiake-1 in #2007).
split_rules::link_miss_scale: the scale is the fastest stage's link over this stage's, applied
only from a 4x gap (a riser or chipset x1/x4 slot beside an x16 one), capped at 64. A symmetric
rig keeps the fitted formula whatever its link speed; the x1 case still gets ~x15.
STRATA_SPLIT_LINK_ABS=1 restores the 0.1.41 rule. SYCL has no link term (unchanged).
Test: split_rules_test (the x1 case, equal gen3 cards, a 2x gap, caps, unprobed stages).
Not run on the reporter's T10s: the reply asks for the 'link ... -> miss cost' lines.
On two equal cards every K whose caches hold all the profiled pairs predicts the same window
time, and the search kept the first one tried: the smallest K, which gives the last stage (it
also carries the MTP drafter) the most layers and lets its cache fill the card to the reserve.
2x Arc Pro B70 with IQ3_S: auto K=24, CUDA1 at 31.8 of 31.9 GiB, ~11 tok/s; --layer-split 30
~54 tok/s (agnaylor in #1440). A full xe card does not fail an allocation, it moves buffers to
system memory.
The SYCL search now scores every placement it tries with its smallest spare room (a stage's
room after its session minus every expert of its layers) and, among the placements within
STRATA_SPLIT_HEADROOM_TOL (default 0.2%) of the best predicted time, takes the one with the
most (split_rules::pick_with_headroom). A log line names both picks when it moves the split.
STRATA_SPLIT_HEADROOM=0 keeps the old pick. CUDA/HIP placement is unchanged.
Test: split_rules_test (a 48-layer two-card model of the report: plain K=24 with 664 MiB spare
on the last card, headroom K=25 with 1728 MiB; tolerance and tie rules).
A stage with one layer holds a handful of expert slots (a 12 GB 3060: 512), and the
prompt chunk of every card in the pipeline is clamped to what that cache can lend.
When the pick has such a stage, search again among placements that give every
stage at least three layers; keep the new pick and print both and why. With none
startable the first pick stays. Identical cards pick balanced stages and never
reach the second search.
Niko1221