[https://nvbugs/6601537][fix] Set host_cache_size for dsr1_fp4_v2 dep4 1k8k to avoid KV deadlock

[chenfeiz0326]

Root cause

The perf-sanity aggregated case

perf/test_perf_sanity.py::test_e2e[aggr_upload-deepseek_r1_fp4_v2_grace_blackwell-r1_fp4_v2_dep4_mtp1_1k8k]

dies on GB200 before a single request completes, with a KV-cache-manager-v2
scheduler deadlock (scheduler_v2.py:447):

RuntimeError: V2 scheduler deadlock: 512 generation request(s) active but none
could be scheduled or evicted. KV cache pool is likely exhausted with no host
cache tier for suspend/resume offload. Configure kv_cache_config.host_cache_size
or increase kv_cache_config.max_tokens.

The problem is the size of the auto-provisioned host cache tier, not a missing
one. That distinction matters, because the quoted sentence invites the wrong
diagnosis: its wording is fixed prose (only the request count is interpolated),
so "with no host cache tier" is not an observation about the run. In the failing
log the tier was in fact provisioned — the auto-sizing line is present, and there
are zero occurrences of Retrying without host cache tier and zero
cuMemHostRegister errors.

With host_cache_size unset, _compute_auto_host_tier_quota() "defaults to the
device quota, capped by the per-node available-memory budget shared with
co-located ranks and by the pinnable-memory (RLIMIT_MEMLOCK) limit". On the
failing run those three terms were:

term	value	source
device quota	39.29 GiB	max_gpu_total_bytes = 42187585126
mem_available / local_ranks * 0.5	50.71 GiB	logged available host memory 405.69GiB, 4 co-located ranks
RLIMIT_MEMLOCK * 0.8	unlimited	—
host tier = min(...)	39.29 GiB	bound by the device term

The three inputs are logged; the resulting quota is not, so that last step
follows from the documented rule rather than from a log line. The consequence is
that total tier capacity cannot exceed 2x the device pool — 78.58 GiB here.

This config drives concurrency: 2048 over 4 attention-DP ranks
(max_batch_size: 512 each) at isl=1024 / osl=8192. The suspend/resume
overflow does not fit in that combined budget, so the scheduler correctly trips
its designed deadlock guard rather than corrupting state.

Fix

Set an explicit host_cache_size on the one affected server_config. An explicit
value is used verbatim, bypassing the device-derived default and its caps.

     kv_cache_config:
       dtype: 'fp8'
       enable_block_reuse: false
       free_gpu_memory_fraction: 0.8
+      host_cache_size: 128849018880
     speculative_config:
       decoding_type: 'MTP'

128849018880 = 120 GiB, comfortably above the 78.58 GiB the auto path could
reach. The workload itself is untouched — concurrency stays at 2048, iterations
at 5, max_batch_size at 512.

Why a large value is safe here

The quota is a ceiling, not a reservation. The nominal 4 x 120 GiB = 480 GiB
was never resident: measured peak host RSS for the whole 4-rank step was
153.90 GiB on a node with 918 GiB RealMemory, and the run logged no
host-memory error. Pages are pinned as the suspend/resume path actually needs
them.

Before / after evidence

Both runs are commit 3253b640 on 4x GB200 (lyris, 1 node) and reused the
same prebuilt wheel (tensorrt_llm-1.3.0rc25, BUILD_WHEEL=false) with the
same scheduler config (GUARANTEED_NO_EVICT, max_util_for_resume=0.95), so
host_cache_size is the only variable that changed.

	before (host_cache_size unset)	after (this change)
Slurm job	2734993	2744049
Outcome	CANCELLED, elapsed 00:18:04	COMPLETED, elapsed 01:30:21
Failure	deadlock at 08/19 01:44:23, broadcast to 2048 pending requests	none — zero V2 scheduler deadlock occurrences
Requests	no accounting produced (metric_value=null)	10240 total, 10240 successful, 0 failed
Throughput	none	20583.92 tok/s over 4584.74 s
Peak host RSS	67.32 GiB	153.90 GiB

The effective server config in the passing run confirms the value propagated
through the perf-sanity YAML rather than being injected by hand — the harness's
generated extra-llm-api-config.aggr.r1_fp4_v2_dep4_mtp1_1k8k.yml contains
kv_cache_config.host_cache_size: 128849018880 in exactly the slot this diff
adds, and the runtime dump shows
KvCacheConfig(..., host_cache_size=128849018880, ...).

Scope

• Category: kvcache-v2-scheduler-deadlock (1 case)
• Parent NVBug: 6601537
• Files touched: tests/scripts/perf-sanity/aggregated/deepseek_r1_fp4_v2_grace_blackwell.yaml
  (the fix, 1 line) and tests/integration/test_lists/waives.txt (the unwaive,
  1 line removed)

Only the r1_fp4_v2_dep4_mtp1_1k8k server_config is modified; the other eight
server_configs in the file are untouched.

This PR also removes the case's waive line from
tests/integration/test_lists/waives.txt, so the fixed case returns to
pre-merge CI in the same change that fixes it. The waiver is what stopped every
pre-merge stage from exercising this config, so landing the fix while it stayed
in place would ship with no CI coverage. Only this case's line is removed; the
sibling perf-sanity waivers are untouched.

Test Coverage

perf/test_perf_sanity.py::test_e2e[aggr_upload-deepseek_r1_fp4_v2_grace_blackwell-r1_fp4_v2_dep4_mtp1_1k8k],
re-run manually on 4x GB200 (job 2744049) with this change applied: 10240/10240
requests successful, 0 failed, 20583.92 tok/s.

Note for KVCM-V2 owners (no action required in this PR)

Two observations from this investigation that outlive the config fix:

1. Because the auto host tier defaults to the device quota, total KV capacity
   is bounded at 2x the device pool for any V2 user who does not set
   host_cache_size. A workload admitted on device-pool sizing can therefore
   deadlock rather than degrade. Decoupling that default, or bounding admission
   by the actual tier capacity, would fix the class rather than this instance.
2. The deadlock message's with no host cache tier clause is emitted even when a
   tier is present and correctly sized, which points readers away from the real
   cause. Reporting the resolved tier quota (and which term bound it) in that
   message — or in the auto-sizing log line, which currently logs its inputs but
   not its result — would have made this a one-look diagnosis.

Also worth noting: this config requests GUARANTEED_NO_EVICT yet fails inside
the suspend/resume path, which is reached via the MAX_UTILIZATION behavior the
host tier backs.

PR Checklist

• Commit is DCO signed-off (git commit -s)
• Change is minimal and confined to the one affected server_config
• No test-infra edits, no threshold relaxation, no pytest.skip, no
  disabled optimizations, no workload reduction (concurrency stays 2048)
• Verified by re-running the failing case on real GPUs

Dev Engineer Review

• The change sets kv_cache_config.host_cache_size to 128849018880 bytes (120 GiB) for r1_fp4_v2_dep4_mtp1_1k8k.
• The value addresses the device-derived 39.29 GiB limit and prevents the KVCM-V2 scheduler deadlock.
• The scope is limited to one server configuration.
• The waiver entry was removed from tests/integration/test_lists/waives.txt.
• The manual 4x GB200 rerun succeeded with 10,240/10,240 requests and 20,583.92 tok/s.

QA Engineer Review

• Removed one skipped performance sanity test entry from tests/integration/test_lists/waives.txt.
• No test-db/ or qa/ files were modified.
• CBTS coverage data is unavailable.
• Verdict: needs follow-up.

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Walkthrough

The performance sanity configuration adds a 128849018880-byte host cache size to the 1k8k DEP4/MTP1 KV-cache settings and removes the matching test waiver.

Changes

Performance configuration

Layer / File(s)	Summary
Configure and enable performance test tests/scripts/perf-sanity/aggregated/deepseek_r1_fp4_v2_grace_blackwell.yaml, tests/integration/test_lists/waives.txt	The 1k8k DEP4/MTP1 configuration sets host_cache_size to 128849018880 bytes. The matching performance sanity test is no longer skipped.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to ba87c

The affected performance test now uses an explicit host-cache size and is returned to pre-merge coverage; no actionable merge-blocking risk remains after normal checks and review.

Possibly related PRs

• NVIDIA/TensorRT-LLM#17649: Removes another stale performance-test waiver.
• NVIDIA/TensorRT-LLM#17962: Targets a related DeepSeek performance-sanity waiver and KV-cache setting.
• NVIDIA/TensorRT-LLM#17967: Removes related DeepSeek performance-sanity waivers.

Suggested reviewers: dc3671, dhansen-nvidia

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the NVBugs fix, the affected configuration, and the host cache change that prevents the KV deadlock.
Description check	✅ Passed	The description explains the root cause, fix, scope, test coverage, results, and checklist with sufficient detail.

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Actionable comments posted: 1

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Inline comments:
In
`@tests/scripts/perf-sanity/aggregated/deepseek_r1_fp4_v2_grace_blackwell.yaml`:
- Line 236: Add the standard NVIDIA copyright header with year 2026 at the top
of the configuration file containing host_cache_size, without changing the
existing configuration values.

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