leavelet
4e9b4d05c0
A CP4 prefill server hung 79s in _plan_cp_load_back_owner_lane_evictions (the [HiCache-load]
slow-scan) and was killed by the detokenizer health-check. Root cause (verified from the b300
hang log + code): the L1 free-room watermark (--hicache-l1-free-room-ratio 0.25 over a 31507-page
lane) hands the planner a ~7877-page single-owner deficit; the planner then rescans all ~2000
evictable candidates once per victim (~195 iters), and for EACH candidate every iteration it
recomputes _cp_load_back_node_owner_page_counts -- which under the pooled shared-L2 path (no
page_owners on CpSharedL2NodeMetadata) takes the device-tensor fallback and does cp_size per-owner
.item() device->host syncs. That is ~195 * 2000 * 4 ~= 1.5M CUDA syncs on the synchronous load-back
admission path, blocking the scheduler for ~79s.
Fix (byte-identical victim selection, just fast):
- Memoize the owner-count histogram per planning call ({node.id: counts}); the counts are invariant
while node.value is fixed (the plan does not mutate values), so node.id is a safe key for the plan's
duration. Threaded explicitly to both call sites (planner loop + ancestor-unlock helper). Turns
O(victims*candidates) recomputes into O(distinct nodes).
- Replace the cp_size per-owner sum().item() loop with one bincount().tolist() device->host sync.
Net: ~79s -> ~1s; the eviction plan (victims, planned_freed) is unchanged. bincount == the per-owner
loop proven over 8000 random vectors incl. the (-1)%cp==cp-1 zero-loc edge. New memo regression test;
existing count-fn + planner tests pass (the one pre-existing unrelated EAGLE-tail failure is unchanged).
(The 7877-page watermark magnitude is a separate, config-side issue: --hicache-l1-free-room-ratio 0.25
reserves ~25% of a ~2M-token lane -- ~30x more than a 64K chunk needs; lower it.)
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Unit Tests
Component-level tests that do not launch a server or load model weights. Tests can use CPU or GPU — the key criterion is no server process.
Quick Start
- Find the source file under
python/sglang/srt/. - Create the corresponding test here, mirroring the source tree:
srt/mem_cache/radix_cache.py → unit/mem_cache/test_radix_cache.py srt/sampling/sampling_params.py → unit/sampling/test_sampling_params.py - Register for CI at the top of the file (after imports, before test classes):
from sglang.test.ci.ci_register import register_cpu_ci register_cpu_ci(est_time=5, suite="stage-a-test-cpu") # or: register_cuda_ci(est_time=10, suite="stage-b-test-1-gpu-small") - Run locally:
pytest test/registered/unit/ -v # all unit tests pytest test/registered/unit/mem_cache/ -v # one module - Run with coverage:
# summary pytest test/registered/unit/ --cov --cov-config=.coveragerc -v # PR incremental check (require ≥60% on changed lines) pytest test/registered/unit/ --cov --cov-config=.coveragerc --cov-report=xml diff-cover coverage.xml --compare-branch=origin/main --fail-under=60
Example
"""Unit tests for <module> — no server, no model loading."""
from sglang.test.ci.ci_register import register_cpu_ci
register_cpu_ci(est_time=5, suite="stage-a-test-cpu")
import unittest
from sglang.srt.<module> import TargetClass
from sglang.test.test_utils import CustomTestCase
class TestTargetClass(CustomTestCase):
def test_basic_behavior(self):
obj = TargetClass(...)
self.assertEqual(obj.method(), expected)
if __name__ == "__main__":
unittest.main()
Rules
- No
popen_launch_server()orEngine(...). - No model weight loading.
- Use
CustomTestCase(fromsglang.test.test_utils, adds CI retry). - Use
unittest.mockfor dependencies that are expensive to construct.