### What this PR does / why we need it?
This PR introduces a "balance scheduling" feature, enabled by the
`VLLM_ASCEND_BALANCE_SCHEDULING` environment variable. This feature
adjusts the scheduling logic to better balance the load across
data-parallel workers, preventing a single worker from blocking
scheduling for others. This can improve overall throughput.
Additionally, this PR includes a number of other updates and fixes to
the scheduler, syncing it with a more recent version of the upstream
vLLM scheduler. These changes include:
- Handling for paused scheduler state.
- Support for Mamba block-aligned splits.
- Handling for streaming requests.
- Refinements in preemption logic and resource management (KV cache,
encoder cache).
- General code refactoring for clarity and correctness.
Fixes #
### Does this PR introduce _any_ user-facing change?
Yes, this PR introduces a new feature controlled by the
`VLLM_ASCEND_BALANCE_SCHEDULING` environment variable. When enabled, the
scheduling behavior changes, which could affect performance and request
throughput.
### How was this patch tested?
CI passed. Further testing should be done to validate the performance
and correctness of the new scheduling logic under various workloads,
with and without the feature flag enabled.
Signed-off-by: GDzhu01 <809721801@qq.com>
### What this PR does / why we need it?
This PR fixes the logger initialization in patches so that the log info
can be displayed as expected.
### Does this PR introduce _any_ user-facing change?
No.
- vLLM version: v0.17.0
- vLLM main:
4497431df6
---------
Signed-off-by: Angazenn <supperccell@163.com>
### Motivation.
**Limitations of the current vLLM v1 scheduling strategy**
vLLM v1 scheduling currently enables chunkedprefill by default, which
processes prefill and decode requests simultaneously in a single
scheduling session. This can impact the overall system throughput and
performance in some scenarios.
Balance scheduling addresses this issue by synchronizing the number of
running queues across all schedulers to delay the scheduling of new
requests, thereby improving the overall system's steady-state decoding
time. This achieves:
✅Adding `balance_gather` to the scheduler synchronizes the number of
requests in the running queues between DPs.
✅Balance scheduling improves the decode steady-state time, thereby
increasing the overall output throughput of the inference system.
### Proposed Change.
**1.Feature Overview**
In the vLLM scheduler, running requests (i.e., requests that are already
undergoing pre-filled computation) have the highest priority, followed
by waiting requests (i.e., requests that have not yet been computed).
As shown in the diagram above, when the entire inference system exits
from a steady state, the scheduler will schedule a batch of new requests
for prefill operations and then synchronize them among the dynamic
programming (DP) models. This can cause some DP models that are entirely
decoded to synchronize with the number of prefilled tokens. Frequent
prefill scheduling by certain DP models can lead to a deterioration in
the overall system output throughput.
Balance scheduling synchronizes the number of running queue requests
across different DPs, and only schedules new requests for prefilling
when at least every scheduler has fewer than max_nun_requst.
**2.Implementation Design**
**3.Experiment Results**
- Fixed-length input scenario: In the performance test scenario with
3.5K fixed-length input and 1.5K fixed-length output, the throughput
performance was improved by approximately **18%** after adding balance
scheduling.
| Method | Model | Input Len | Request Count | Output Len | BatchSize |
Average TTFT | Average TPOT | e2e duration | Input Token Throughput |
Output Token Throughput | Request Throughput
| ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |
---- | ---- |
| Baseline | DeepSeekV3.1 | 3500 | 512 | 1500 | 128 | 6600 | 86.85 |
591.9s | 3030.5 | 1297.3 | 0.86 |
| Balance scheduling | DeepSeekV3.1 | 3500 | 512 | 1500 | 128 | 7012 |
70.63 | 501.7s | 3575.7 | 1530.7 | 1.02 |
**4.Demo PR**
[#29721 ](https://github.com/vllm-project/vllm/pull/29721)
---------
Signed-off-by: GDzhu01 <809721801@qq.com>
