Re: [PATCH 8/8] raid6/kunit: add a benchmark

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The benchmark loop disables preemption for an extended period, risking soft lockups and RCU stalls on slower architectures or emulators.
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--- Patch [8]: [PATCH 8/8] raid6/kunit: add a benchmark ---
commit c8db04a9f21fef60a9c9e7ad0c98848e405330de
Author: Christoph Hellwig <hch@lst.de>

raid6/kunit: add a benchmark

This commit adds a benchmark to test the RAID 6 P/Q functions for more
representative block sizes and numbers of disks. The maximum allocation
size is split to allow benchmarking larger sizes, and results are reported
in GB/s.

> diff --git a/lib/raid/raid6/tests/raid6_kunit.c b/lib/raid/raid6/tests/raid6_kunit.c
> index 9f3e671a12241..7d0a1ec980013 100644
> --- a/lib/raid/raid6/tests/raid6_kunit.c
> +++ b/lib/raid/raid6/tests/raid6_kunit.c
[ ... ]
> @@ -229,6 +230,68 @@ static void raid6_test(struct kunit *test)
[ ... ]
> +static void raid6_benchmark(struct kunit *test)
> +{
[ ... ]
> +		for (j = 0; j < ARRAY_SIZE(len_to_test); j++) {
> +			unsigned int len = len_to_test[j];
> +			const unsigned long num_iters = 1000;
> +
> +			KUNIT_ASSERT_GT(test, len, 0);
> +			KUNIT_ASSERT_LE(test, len, RAID6_KUNIT_ALLOC_BYTES);
> +
> +			preempt_disable();
> +			t = ktime_get_ns();
> +			for (l = 0; l < num_iters; l++)
> +				raid6_gen_syndrome(nr_to_test[i],
> +						len_to_test[j], test_buffers);
> +			t = max(ktime_get_ns() - t, 1);
> +			preempt_enable();

[Severity: Medium]
Is it safe to disable preemption across this entire 1000-iteration loop?

For the maximum test configuration of 32 disks and 16KB buffers, this loop
processes roughly 512MB of data in a single uninterruptible block. On slower
environments like emulators or User-Mode Linux (which are commonly used for
KUnit tests), could this exceed standard watchdog thresholds and trigger soft
lockups or RCU stalls?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260715144825.95432-1-hch@lst.de?part=8