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workqueue: forbid TEST_WORKQUEUE from being built-in

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The benchmark drives the workqueue's affinity_scope through sysfs by
filp_open()'ing /sys/bus/workqueue/devices/bench_wq/affinity_scope. When
CONFIG_TEST_WORKQUEUE=y, the module_init runs during kernel init before
userspace has mounted sysfs, so every open returns -ENOENT and the
benchmark loop spins emitting:

  test_workqueue: open /sys/bus/workqueue/devices/bench_wq/affinity_scope failed: -2

Mirror the TEST_BPF pattern and add "depends on m" so Kconfig will not
let this be built into the kernel image, and document the reason in the
help text.

Fixes: 24b2e73f97 ("workqueue: add test_workqueue benchmark module")
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Breno Leitao 2026-05-11 05:26:55 -07:00 committed by Tejun Heo
parent dfca46365a
commit 1503043fd7
1 changed files with 5 additions and 0 deletions
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lib/Kconfig.debug
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@ -2649,12 +2649,17 @@ config TEST_VMALLOC
config TEST_WORKQUEUE
tristate "Test module for stress/performance analysis of workqueue"
depends on m
default n
help
This builds the "test_workqueue" module for benchmarking
workqueue throughput under contention. Useful for evaluating
affinity scope changes (e.g., cache_shard vs cache).
The test drives sysfs to switch affinity scopes, so it must be
loaded after userspace has mounted sysfs; building it in (=y)
would run module_init before /sys is available.
If unsure, say N.
config TEST_BPF