linux-kernel - Re: [PATCH v2 2/6] kunit: move check if assertion passed into the macros

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Message-ID: <CABVgOSnpGBsm9nONGyKkNFOb8ycxnt4pe4P65R7Gp0eYBJW9pA@mail.gmail.com>
Date:   Wed, 12 Jan 2022 09:27:13 +0800
From:   David Gow <davidgow@...gle.com>
To:     Daniel Latypov <dlatypov@...gle.com>
Cc:     brendanhiggins@...gle.com, linux-kernel@...r.kernel.org,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        skhan@...uxfoundation.org, torvalds@...ux-foundation.org
Subject: Re: [PATCH v2 2/6] kunit: move check if assertion passed into the macros

On Wed, Jan 12, 2022 at 3:42 AM Daniel Latypov <dlatypov@...gle.com> wrote:
>
> Currently the code always calls kunit_do_assertion() even though it does
> nothing when `pass` is true.
>
> This change moves the `if(!(pass))` check into the macro instead
> and renames the function to kunit_do_failed_assertion().
> I feel this a  bit easier to read and understand.
>
> This has the potential upside of avoiding a function call that does
> nothing most of the time (assuming your tests are passing) but comes
> with the downside of generating a bit more code and branches. We try to
> mitigate the branches by tagging them with `unlikely()`.
>
> This also means we don't have to initialize structs that we don't need,
> which will become a tiny bit more expensive if we switch over to using
> static variables to try and reduce stack usage. (There's runtime code
> to check if the variable has been initialized yet or not).
>
> Signed-off-by: Daniel Latypov <dlatypov@...gle.com>
> Reviewed-by: Brendan Higgins <brendanhiggins@...gle.com>
> ---

This looks good. I'm still not 100% sold that putting the if() outside
the function is significantly easier to read, but I don't think it's
harder to read either, and getting rid of the function call is
probably worth it.

Reviewed-by: David Gow <davidgow@...gle.com>

-- David

>  include/kunit/test.h | 21 +++++++++++----------
>  lib/kunit/test.c     | 13 ++++---------
>  2 files changed, 15 insertions(+), 19 deletions(-)
>
> diff --git a/include/kunit/test.h b/include/kunit/test.h
> index b26400731c02..12cabd15449a 100644
> --- a/include/kunit/test.h
> +++ b/include/kunit/test.h
> @@ -12,6 +12,7 @@
>  #include <kunit/assert.h>
>  #include <kunit/try-catch.h>
>
> +#include <linux/compiler.h>
>  #include <linux/container_of.h>
>  #include <linux/err.h>
>  #include <linux/init.h>
> @@ -770,18 +771,18 @@ void __printf(2, 3) kunit_log_append(char *log, const char *fmt, ...);
>   */
>  #define KUNIT_SUCCEED(test) do {} while (0)
>
> -void kunit_do_assertion(struct kunit *test,
> -                       struct kunit_assert *assert,
> -                       bool pass,
> -                       const char *fmt, ...);
> +void kunit_do_failed_assertion(struct kunit *test,
> +                              struct kunit_assert *assert,
> +                              const char *fmt, ...);
>
>  #define KUNIT_ASSERTION(test, pass, assert_class, INITIALIZER, fmt, ...) do {  \
> -       struct assert_class __assertion = INITIALIZER;                         \
> -       kunit_do_assertion(test,                                               \
> -                          &__assertion.assert,                                \
> -                          pass,                                               \
> -                          fmt,                                                \
> -                          ##__VA_ARGS__);                                     \
> +       if (unlikely(!(pass))) {                                               \
> +               struct assert_class __assertion = INITIALIZER;                 \
> +               kunit_do_failed_assertion(test,                                \
> +                                         &__assertion.assert,                 \
> +                                         fmt,                                 \
> +                                         ##__VA_ARGS__);                      \
> +       }                                                                      \
>  } while (0)
>
>
> diff --git a/lib/kunit/test.c b/lib/kunit/test.c
> index c7ed4aabec04..3a52c321c280 100644
> --- a/lib/kunit/test.c
> +++ b/lib/kunit/test.c
> @@ -275,16 +275,11 @@ static void __noreturn kunit_abort(struct kunit *test)
>         WARN_ONCE(true, "Throw could not abort from test!\n");
>  }
>
> -void kunit_do_assertion(struct kunit *test,
> -                       struct kunit_assert *assert,
> -                       bool pass,
> -                       const char *fmt, ...)
> +void kunit_do_failed_assertion(struct kunit *test,
> +                              struct kunit_assert *assert,
> +                              const char *fmt, ...)
>  {
>         va_list args;
> -
> -       if (pass)
> -               return;
> -
>         va_start(args, fmt);
>
>         assert->message.fmt = fmt;
> @@ -297,7 +292,7 @@ void kunit_do_assertion(struct kunit *test,
>         if (assert->type == KUNIT_ASSERTION)
>                 kunit_abort(test);
>  }
> -EXPORT_SYMBOL_GPL(kunit_do_assertion);
> +EXPORT_SYMBOL_GPL(kunit_do_failed_assertion);
>
>  void kunit_init_test(struct kunit *test, const char *name, char *log)
>  {
> --
> 2.34.1.575.g55b058a8bb-goog
>