Re: [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression

[David Gow]

Le 20/04/2026 à 8:28 PM, Albert Esteve a écrit :
> From: Alessandro Carminati <acarmina@xxxxxxxxxx>
>
> KUnit support is not consistently present across distributions, some
> include it in their stock kernels, while others do not.
> While both KUNIT and KUNIT_SUPPRESS_BACKTRACE can be considered debug
> features, the fact that some distros ship with KUnit enabled means it's
> important to minimize the runtime impact of this patch.
>
> To that end, this patch adds an atomic counter that tracks the number
> of active suppressions. __kunit_is_suppressed_warning() checks this
> counter first and returns immediately when no suppressions are active,
> avoiding RCU-protected list traversal in the common case.
>
> Signed-off-by: Alessandro Carminati <acarmina@xxxxxxxxxx>
> Signed-off-by: Albert Esteve <aesteve@xxxxxxxxxx>
> ---

I'm not sure how much of an improvement this is.

It might be worth putting things behind the kunit_running static branch.

You could even add a new kunit_has_suppressed_warnings static branch, 
though I doubt anyone's too worried about the runtime performance of 
WARN() during testing, but with no suppressions, so it's likely not 
worth it.

Have a look at, e.g., kunit_fail_current_test() in 
include/kunit/test-bug.h, which uses the existing hooks implementation 
and static branch to reduce the overhead as much as I'd expect we need. 
That'd also potentially let you move the backtrace suppression code into 
the kunit.ko module, so you're not even paying more than ~a pointer's 
worth of memory if no tests are even loaded.

Cheers,
-- David