Re: [RFC PATCH v24 10/10] lib: add a benchmark of hierarchical per-cpu counters

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] lib: missing kernel-parameters.txt entry for
  percpu_counter_tree_bench.batch
--

commit 88946339b389754c894fb27102ddde74cdda534f
Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

lib: add a benchmark of hierarchical per-cpu counters

This commit adds a KUnit benchmark comparing hierarchical per-CPU counters
against struct percpu_counter across update, lifecycle, and churn workloads.
It also introduces the CONFIG_PERCPU_COUNTER_TREE_BENCH option and a batch
module parameter to configure the counter batch size.

> diff --git a/lib/Kconfig b/lib/Kconfig
> index 3921177a0d243..6ab9644a4cb83 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -53,6 +53,21 @@ config PERCPU_COUNTER_TREE_KUNIT_TEST
>  
>  	  When in doubt, say N.
>  
> +config PERCPU_COUNTER_TREE_BENCH
> +	tristate "Benchmark of hierarchical per-cpu counters"
> +	depends on KUNIT && SMP
> +	help
> +	  This builds a KUnit benchmark comparing the hierarchical per-cpu
> +	  counters with struct percpu_counter: update cost with all online
> +	  CPUs updating shared and private counters, and init/destroy cost.
> +	  It runs for a few minutes on large machines.
> +
> +	  The batch size and the tree shape can be changed with the
> +	  percpu_counter_tree_bench.batch= and percpu_counter_tree.arity=
> +	  parameters, see lib/tests/percpu_counter_tree_bench.c.

[ ... ]

> diff --git a/lib/tests/percpu_counter_tree_bench.c b/lib/tests/percpu_counter_tree_bench.c
> new file mode 100644
> index 0000000000000..e041ba8ba8c74
> --- /dev/null
> +++ b/lib/tests/percpu_counter_tree_bench.c
> @@ -0,0 +1,610 @@

[ ... ]

> +/* Like the RSS counters by default. */
> +static unsigned int batch = 32;
> +module_param(batch, uint, 0444);
> +MODULE_PARM_DESC(batch, "Batch size of the hierarchical counters (power of 2, 2 to 128)");

[Severity: Low]
As reported by Sashiko on RFC v23 [1], lib/tests/percpu_counter_tree_bench.c
defines the batch module parameter via module_param(batch, uint, 0444) under
CONFIG_PERCPU_COUNTER_TREE_BENCH, and both the commit description and the
PERCPU_COUNTER_TREE_BENCH help text in lib/Kconfig advertise setting
percpu_counter_tree_bench.batch= on the kernel command line at boot alongside
percpu_counter_tree.arity=.

Should percpu_counter_tree_bench.batch= also be documented in
Documentation/admin-guide/kernel-parameters.txt?

[1] https://lore.kernel.org/r/20261102190708.1287100-11-mathieu.desnoyers@efficios.com

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261105203639.1459524-1-mathieu.desnoyers@efficios.com?part=10