From: Pravin Pathak <[email protected]>
This series introduces the Software Load Balancer (SLB) Eventdev PMD
(`event_slb`) supporting parallel, atomic and ordered queues. It is
a distributed software scheduler that scales well.
Motivation
----------
Existing software eventdev PMDs face trade-offs between centralized
bottlenecks and feature coverage:
- `event_sw` relies on a dedicated centralized scheduler consuming
an extra CPU core. The single scheduling core also limits maximum
throughput and it does not scale.
- `event_dsw` distributes scheduling across worker cores without a
central scheduler core, but does not support ordered queues and
incurs per-port control ring messaging overhead during atomic flow
migrations. It also does not support service priority.
Design Overview
---------------
`event_slb` is a distributed (`RTE_EVENT_DEV_CAP_DISTRIBUTED_SCHED`),
maintenance-free (`RTE_EVENT_DEV_CAP_MAINTENANCE_FREE`) software eventdev
PMD that supports Atomic, Ordered, Parallel, and Single-Link queues:
1. Queue-Centric Ring Architecture:
- Parallel and Single-Link queues map directly to `rte_event_ring`
instances (MP/MC for parallel, MP/SC for single-link), allowing
zero-copy burst enqueue and dequeue without history tracking.
- Ordered queues use the ring slot index at dequeue time as an implicit
sequence number into a per-queue reorder buffer, draining contiguous
completed events in order without global sequence counters. This
makes ordered queue implementaion highly efficient performing close
to parallel queues.
- Atomic queues use a main MP/SC queue ring alongside per-port SP/SC
rings and a 2048-entry flow-to-port affinity table. All cores
served by the atomic queue are used for scheduling.
2. Lock-Free / Zero-Pause Atomic Flow Migration:
- When an atomic queue refills per-port rings and detects persistent
congestion on a destination port, SLB selects the lightest flow on
that port (outside the migration cooldown window) and waits for
queues in-flight events to drain naturally before switching the
flow's port affinity and schedule hold-buffer entries.
- Hold buffer is used for buffering events towards migrating ports
while allowing serving other ports.
- Implementaion avoids cross-port pause/unpause control rings while
preserving strict per-flow ordering.
3. Credit-Based Backpressure & Priority Scheduling:
- A global atomic credit pool with per-port local credit caches bounds
total in-flight events (`nb_events_limit`) and enforces
`new_event_threshold` with minimal atomic contention.
- Ports support two strict service priority levels with
round-robin scheduling within each priority level.
4. Observability & Testing:
- Device and per-port/per-queue extended statistics (`xstats`),
detailed `rte_event_dev_dump()` diagnostics, and a unit self-test
suite (`eventdev_selftest_slb`) covering parallel, atomic, ordered,
single-link, priority, backpressure, stop-flush, and multi-core
atomic migration scenarios.
5. Future Plan:
- Supporting Event priority
- Optimizing atomic flow migration
Pravin Pathak (8):
event/slb: introduce software load balancer PMD
event/slb: add support for ordered queues
event/slb: add support for atomic queues
event/slb: add dynamic flow migration for atomic queues
event/slb: add extended statistics and diagnostics
event/slb: add self-test and documentation
event/slb: update resets and credit defaults
event/slb: improve port linking, config checks and atomic refill
MAINTAINERS | 6 +
app/test/test_eventdev.c | 7 +
doc/guides/eventdevs/features/slb.ini | 25 +
doc/guides/eventdevs/index.rst | 1 +
doc/guides/eventdevs/slb.rst | 61 ++
drivers/event/meson.build | 1 +
drivers/event/slb/meson.build | 21 +
drivers/event/slb/slb_evdev.c | 904 ++++++++++++++++++
drivers/event/slb/slb_evdev.h | 263 ++++++
drivers/event/slb/slb_event.c | 1219 +++++++++++++++++++++++++
drivers/event/slb/slb_selftest.c | 522 +++++++++++
drivers/event/slb/slb_xstats.c | 347 +++++++
12 files changed, 3377 insertions(+)
create mode 100644 doc/guides/eventdevs/features/slb.ini
create mode 100644 doc/guides/eventdevs/slb.rst
create mode 100644 drivers/event/slb/meson.build
create mode 100644 drivers/event/slb/slb_evdev.c
create mode 100644 drivers/event/slb/slb_evdev.h
create mode 100644 drivers/event/slb/slb_event.c
create mode 100644 drivers/event/slb/slb_selftest.c
create mode 100644 drivers/event/slb/slb_xstats.c
--
2.53.0
