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From:   Daniel Latypov <dlatypov@google.com>
Date:   Wed, 21 Oct 2020 10:47:50 -0700
Message-ID: <CAGS_qxpX0Do+z-wzCC=twbt-htL=Jkqvrk4L4rKTtXFPfX-TCA@mail.gmail.com>
Subject: Re: [PATCH] lib: add basic KUnit test for lib/math
To:     David Gow <davidgow@google.com>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Brendan Higgins <brendanhiggins@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Shuah Khan <skhan@linuxfoundation.org>
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On Tue, Oct 20, 2020 at 8:40 PM David Gow <davidgow@google.com> wrote:
>
> On Tue, Oct 20, 2020 at 6:46 AM Daniel Latypov <dlatypov@google.com> wrote:
> >
> > Add basic test coverage for files that don't require any config options:
> > * gcd.c
> > * lcm.c
> > * int_sqrt.c
> > * reciprocal_div.c
> > (Ignored int_pow.c since it's a simple textbook algorithm.)
> >
> I don't see a particular reason why int_pow.c being a simple algorithm
> means it shouldn't be tested. I'm not saying it has to be tested by
> this particular change -- and I doubt the test would be
> earth-shatteringly interesting -- but there's no real reason against
> testing it.

Agreed on principle, but int_pow() feels like a special case.
I've written it the exact same way (modulo variable names+types)
several times in personal projects.
Even the spacing matched exactly in a few of those...

>
> > These tests aren't particularly interesting, but
> > * they're chosen as easy to understand examples of how to write tests
> > * provides a place to add tests for any new files in this dir
> > * written so adding new test cases to cover edge cases should be easy
>
> I think these tests can stand on their own merits, rather than just as
> examples (though I do think they do make good additional examples for
> how to test these sorts of functions).
> So, I'd treat this as an actual test of the maths functions (and
> you've got what seems to me a decent set of test cases for that,
> though there are a couple of comments below) first, and any use it
> gains as an example is sort-of secondary to that (anything that makes
> it a better example is likely to make it a better test anyway).
>
> In any case, modulo the comments below, this seems good to me.

Ack.
I'll wait on Andy's input before deciding whether or not to push out a
v2 with the changes.

>
> -- David
>
> > Signed-off-by: Daniel Latypov <dlatypov@google.com>
> > ---
> >  lib/math/Kconfig     |   5 ++
> >  lib/math/Makefile    |   2 +
> >  lib/math/math_test.c | 197 +++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 204 insertions(+)
> >  create mode 100644 lib/math/math_test.c
> >
> > diff --git a/lib/math/Kconfig b/lib/math/Kconfig
> > index f19bc9734fa7..6ba8680439c1 100644
> > --- a/lib/math/Kconfig
> > +++ b/lib/math/Kconfig
> > @@ -15,3 +15,8 @@ config PRIME_NUMBERS
> >
> >  config RATIONAL
> >         bool
> > +
> > +config MATH_KUNIT_TEST
> > +       tristate "KUnit test for lib/math" if !KUNIT_ALL_TESTS
> > +       default KUNIT_ALL_TESTS
> > +       depends on KUNIT
> > diff --git a/lib/math/Makefile b/lib/math/Makefile
> > index be6909e943bd..fba6fe90f50b 100644
> > --- a/lib/math/Makefile
> > +++ b/lib/math/Makefile
> > @@ -4,3 +4,5 @@ obj-y += div64.o gcd.o lcm.o int_pow.o int_sqrt.o reciprocal_div.o
> >  obj-$(CONFIG_CORDIC)           += cordic.o
> >  obj-$(CONFIG_PRIME_NUMBERS)    += prime_numbers.o
> >  obj-$(CONFIG_RATIONAL)         += rational.o
> > +
> > +obj-$(CONFIG_MATH_KUNIT_TEST)  += math_test.o
> > diff --git a/lib/math/math_test.c b/lib/math/math_test.c
> > new file mode 100644
> > index 000000000000..6f4681ea7c72
> > --- /dev/null
> > +++ b/lib/math/math_test.c
> > @@ -0,0 +1,197 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Simple KUnit suite for math helper funcs that are always enabled.
> > + *
> > + * Copyright (C) 2020, Google LLC.
> > + * Author: Daniel Latypov <dlatypov@google.com>
> > + */
> > +
> > +#include <kunit/test.h>
> > +#include <linux/gcd.h>
> > +#include <linux/kernel.h>
> > +#include <linux/lcm.h>
> > +#include <linux/reciprocal_div.h>
> > +
> > +/* Generic test case for unsigned long inputs. */
> > +struct test_case {
> > +       unsigned long a, b;
> > +       unsigned long result;
> > +};
> > +
> > +static void gcd_test(struct kunit *test)
> > +{
> > +       const char *message_fmt = "gcd(%lu, %lu)";
> > +       int i;
> > +
> > +       struct test_case test_cases[] = {
> > +               {
> > +                       .a = 0, .b = 1,
> > +                       .result = 1,
> > +               },
> > +               {
> > +                       .a = 2, .b = 2,
> > +                       .result = 2,
> > +               },
> > +               {
> > +                       .a = 2, .b = 4,
> > +                       .result = 2,
> > +               },
> > +               {
> > +                       .a = 3, .b = 5,
> > +                       .result = 1,
> > +               },
> > +               {
> > +                       .a = 3*9, .b = 3*5,
> > +                       .result = 3,
> > +               },
> > +               {
> > +                       .a = 3*5*7, .b = 3*5*11,
> > +                       .result = 15,
> > +               },
> > +               {
> > +                       .a = (1 << 21) - 1,
> > +                       .b = (1 << 22) - 1,
>
> It might be worth noting the factors of these (7^2*127*337 and
> 3*23*89*683) in a comment.
> They aren't mersenne primes, if that's what you were going for, though
> they are coprime.

Yes, they aren't primes.
But 2^x-1 2^(x+1)-1 should always be coprime.
So I figured it was an easy way to get "large" coprimes.

I can pick a pair of Mersenne primes (and comment to that effect) if
you think that'd be clearer.

>
> > +                       .result = 1,
> > +               },
> > +       };
> > +
> > +       for (i = 0; i < ARRAY_SIZE(test_cases); ++i) {
> > +               KUNIT_EXPECT_EQ_MSG(test, test_cases[i].result,
> > +                                   gcd(test_cases[i].a, test_cases[i].b),
> > +                                   message_fmt, test_cases[i].a,
> > +                                   test_cases[i].b);
> > +
> > +               /* gcd(a,b) == gcd(b,a) */
> > +               KUNIT_EXPECT_EQ_MSG(test, test_cases[i].result,
> > +                                   gcd(test_cases[i].b, test_cases[i].a),
> > +                                   message_fmt, test_cases[i].b,
> > +                                   test_cases[i].a);
> > +       }
> > +}
> > +
> > +static void lcm_test(struct kunit *test)
> > +{
> > +       const char *message_fmt = "lcm(%lu, %lu)";
> > +       int i;
> > +
> > +       struct test_case test_cases[] = {
> > +               {
> > +                       .a = 0, .b = 1,
> > +                       .result = 0,
> > +               },
> > +               {
> > +                       .a = 1, .b = 2,
> > +                       .result = 2,
> > +               },
> > +               {
> > +                       .a = 2, .b = 2,
> > +                       .result = 2,
> > +               },
> > +               {
> > +                       .a = 3*5, .b = 3*7,
> > +                       .result = 3*5*7,
> > +               },
>
> If you were looking for extra testcases here, one where b < a would be nice.

Good point, added
+               {
+                       .a = 42, .b = 9999,
+                       .result = 0,
+               },

>
> > +       };
> > +
> > +       for (i = 0; i < ARRAY_SIZE(test_cases); ++i) {
> > +               KUNIT_EXPECT_EQ_MSG(test, test_cases[i].result,
> > +                                   lcm(test_cases[i].a, test_cases[i].b),
> > +                                   message_fmt, test_cases[i].a,
> > +                                   test_cases[i].b);
> > +
> > +               /* lcm(a,b) == lcm(b,a) */
> > +               KUNIT_EXPECT_EQ_MSG(test, test_cases[i].result,
> > +                                   lcm(test_cases[i].b, test_cases[i].a),
> > +                                   message_fmt, test_cases[i].b,
> > +                                   test_cases[i].a);
> > +       }
> > +}
> > +
>
> Again, not pushing for it in this test, but lcm_not_zero() could be
> worth testing at some point, too...

Ack.
I'll hold off on adding that for now, since reusing the lcm table
would require basically a copy paste of the internal logic to figure
out what we'd expect in the zero case.
And atm, it doesn't seem interesting enough to add another separate
test case, esp. if there's already concern the lcm test isn't really
worth having.

>
> > +static void int_sqrt_test(struct kunit *test)
> > +{
> > +       const char *message_fmt = "sqrt(%lu)";
> > +       int i;
> > +
> > +       struct test_case test_cases[] = {
> > +               {
> > +                       .a = 0,
> > +                       .result = 0,
> > +               },
> > +               {
> > +                       .a = 1,
> > +                       .result = 1,
> > +               },
> > +               {
> > +                       .a = 4,
> > +                       .result = 2,
> > +               },
> > +               {
> > +                       .a = 5,
> > +                       .result = 2,
> > +               },
> > +               {
> > +                       .a = 8,
> > +                       .result = 2,
> > +               },
> > +               {
> > +                       .a = 1UL >> 32,
> > +                       .result = 1UL >> 16,
>
> As the kernel test robot noted, these are wrong (the shifts go the
> wrong way, 2^32 might not fit in an unsigned long).

Thanks, fixed locally.


>
> > +               },
> > +       };
> > +
> > +       for (i = 0; i < ARRAY_SIZE(test_cases); ++i) {
> > +               KUNIT_EXPECT_EQ_MSG(test, int_sqrt(test_cases[i].a),
> > +                                   test_cases[i].result, message_fmt,
> > +                                   test_cases[i].a);
> > +       }
> > +}
> > +
> > +struct reciprocal_test_case {
> > +       u32 a, b;
> > +       u32 result;
> > +};
> > +
> > +static void reciprocal_div_test(struct kunit *test)
> > +{
> > +       int i;
> > +       struct reciprocal_value rv;
> > +       struct reciprocal_test_case test_cases[] = {
> > +               {
> > +                       .a = 0, .b = 1,
> > +                       .result = 0,
> > +               },
> > +               {
> > +                       .a = 42, .b = 20,
> > +                       .result = 2,
> > +               },
> > +               {
> > +                       .a = (1<<16), .b = (1<<14),
> > +                       .result = 1<<2,
> > +               },
> > +       };
> > +
> > +       for (i = 0; i < ARRAY_SIZE(test_cases); ++i) {
> > +               rv = reciprocal_value(test_cases[i].b);
> > +               KUNIT_EXPECT_EQ_MSG(test, test_cases[i].result,
> > +                                   reciprocal_divide(test_cases[i].a, rv),
> > +                                   "reciprocal_divide(%u, %u)",
> > +                                   test_cases[i].a, test_cases[i].b);
> > +       }
> > +}
> > +
> > +static struct kunit_case math_test_cases[] = {
> > +       KUNIT_CASE(gcd_test),
> > +       KUNIT_CASE(lcm_test),
> > +       KUNIT_CASE(int_sqrt_test),
> > +       KUNIT_CASE(reciprocal_div_test),
> > +       {}
> > +};
> > +
> > +static struct kunit_suite math_test_suite = {
> > +       .name = "lib-math",
> > +       .test_cases = math_test_cases,
> > +};
> > +
> > +kunit_test_suites(&math_test_suite);
> > +
> > +MODULE_LICENSE("GPL v2");
> >
> > base-commit: 7cf726a59435301046250c42131554d9ccc566b8
> > --
> > 2.29.0.rc1.297.gfa9743e501-goog
> >