linux-kernel - Re: [RFC PATCH v1 2/6] lib: Implement find_{first,next,nth}_nor_bit, find_first_andnot

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Message-ID: <Zs9vSkFNLMDsUH9R@yury-ThinkPad>
Date: Wed, 28 Aug 2024 11:41:14 -0700
From: Yury Norov <yury.norov@...il.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org,
	Valentin Schneider <vschneid@...hat.com>,
	Mel Gorman <mgorman@...e.de>, Steven Rostedt <rostedt@...dmis.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ben Segall <bsegall@...gle.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [RFC PATCH v1 2/6] lib: Implement find_{first,next,nth}_nor_bit,
 find_first_andnot_bit

On Wed, Aug 28, 2024 at 02:24:28PM -0400, Mathieu Desnoyers wrote:
> On 2024-08-23 21:19, Yury Norov wrote:
> 
> [...]
> > 
> > If it comes to v2, can you also add some sanity tests for the new API?
> 
> I don't mind extending existing tests to cover my new APIs, but
> I could not find any selftests for the linux/find.h API within the
> kernel tree. Am I missing something ?
> 
> Thanks,
> 
> Mathieu

There's a very poor coverage indeed. Mostly because old find_bit API
is actively used since very long ago, and if broken, the kernel will
likely crash on boot.

For a new API, I try to keep it tested. You can find test_find_nth_bit
in lib/test_bitmap.c as an example.

Also, if you think your new helpers would have a performance impact,
or will be used in hot paths, you can add performance tests in
lib/find_bit_benchmark.c.

Thanks,
Yury