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Message-ID: <20251002025722.3420916-1-rrnewton@gmail.com>
Date: Wed, 1 Oct 2025 22:57:18 -0400
From: Ryan Newton <rrnewton@...il.com>
To: linux-kernel@...r.kernel.org
Cc: tj@...nel.org,
arighi@...dia.com,
newton@...a.com,
Ryan Newton <rrnewton@...il.com>
Subject: [PATCH 0/3] sched_ext: lockless peek operation for DSQs
This allows sched_ext schedulers an inexpensive operation to peek
at the first element in a queue (DSQ), without creating an iterator
and acquiring the lock on that queue.
Note that manual testing has thus far included a modified version of the
example qmap scheduler that exercises peek, as well as a modified
modified LAVD (from the SCX repo) that exercises peek. The attached test
passes >1000 stress tests when run in concurrent VMs, and when run
sequentially on the host kernel. Presently, tested on the below
workstation and server processors.
- AMD Ryzen Threadripper PRO 7975WX 32-Cores
- AMD EPYC 9D64 88-Core Processor
Initial experiments indicate a substantial speedup (on schbench) when
running an SCX scheduler with per-cpu DSQs and peeking each queue to
retrieve the task with the minimum vruntime across all the CPUs.
Ryan Newton (3):
sched_ext: Add lockless peek operation for DSQs
sched_ext: optimize first_task update logic
sched_ext: Add a selftest for scx_bpf_dsq_peek
include/linux/sched/ext.h | 1 +
kernel/sched/ext.c | 55 ++++-
tools/sched_ext/include/scx/common.bpf.h | 1 +
tools/sched_ext/include/scx/compat.bpf.h | 19 ++
tools/testing/selftests/sched_ext/Makefile | 1 +
.../selftests/sched_ext/peek_dsq.bpf.c | 133 +++++++++++++
tools/testing/selftests/sched_ext/peek_dsq.c | 188 ++++++++++++++++++
7 files changed, 396 insertions(+), 2 deletions(-)
create mode 100644 tools/testing/selftests/sched_ext/peek_dsq.bpf.c
create mode 100644 tools/testing/selftests/sched_ext/peek_dsq.c
--
2.51.0
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