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Message-ID: <q51q92o9-s77q-9431-nss5-03o1258803n0@onlyvoer.pbz>
Date: Sat, 14 Jun 2025 11:25:35 -0400 (EDT)
From: Nicolas Pitre <npitre@...libre.com>
To: David Laight <david.laight.linux@...il.com>
cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
u.kleine-koenig@...libre.com, Oleg Nesterov <oleg@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH v3 next 06/10] lib: test_mul_u64_u64_div_u64: Test both
generic and arch versions
On Sat, 14 Jun 2025, David Laight wrote:
> Change the #if in div64.c so that test_mul_u64_u64_div_u64.c
> can compile and test the generic version (including the 'long multiply')
> on architectures (eg amd64) that define their own copy.
Please also include some explanation for iter_div_u64_rem.
> Test the kernel version and the locally compiled version on all arch.
> Output the time taken (in ns) on the 'test completed' trace.
>
> For reference, on my zen 5, the optimised version takes ~220ns and the
> generic version ~3350ns.
> Using the native multiply saves ~200ns and adding back the ilog2() 'optimisation'
> test adds ~50ms.
>
> Signed-off-by: David Laight <david.laight.linux@...il.com>
Reviewed-by: Nicolas Pitre <npitre@...libre.com>
> ---
>
> New patch for v3, replacing changes in v1 that were removed for v2.
>
> lib/math/div64.c | 8 +++--
> lib/math/test_mul_u64_u64_div_u64.c | 48 ++++++++++++++++++++++++-----
> 2 files changed, 47 insertions(+), 9 deletions(-)
>
> diff --git a/lib/math/div64.c b/lib/math/div64.c
> index 7850cc0a7596..22433e5565c4 100644
> --- a/lib/math/div64.c
> +++ b/lib/math/div64.c
> @@ -178,13 +178,15 @@ EXPORT_SYMBOL(div64_s64);
> * Iterative div/mod for use when dividend is not expected to be much
> * bigger than divisor.
> */
> +#ifndef iter_div_u64_rem
> u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
> {
> return __iter_div_u64_rem(dividend, divisor, remainder);
> }
> EXPORT_SYMBOL(iter_div_u64_rem);
> +#endif
>
> -#ifndef mul_u64_add_u64_div_u64
> +#if !defined(mul_u64_add_u64_div_u64) || defined(test_mul_u64_add_u64_div_u64)
> u64 mul_u64_add_u64_div_u64(u64 a, u64 b, u64 c, u64 d)
> {
> if (WARN_ONCE(!d, "%s: division of (%#llx * %#llx + %#llx) by zero, returning 0",
> @@ -196,7 +198,7 @@ u64 mul_u64_add_u64_div_u64(u64 a, u64 b, u64 c, u64 d)
> return 0;
> }
>
> -#if defined(__SIZEOF_INT128__)
> +#if defined(__SIZEOF_INT128__) && !defined(test_mul_u64_add_u64_div_u64)
>
> /* native 64x64=128 bits multiplication */
> u128 prod = (u128)a * b + c;
> @@ -270,5 +272,7 @@ u64 mul_u64_add_u64_div_u64(u64 a, u64 b, u64 c, u64 d)
>
> return res;
> }
> +#if !defined(test_mul_u64_add_u64_div_u64)
> EXPORT_SYMBOL(mul_u64_add_u64_div_u64);
> #endif
> +#endif
> diff --git a/lib/math/test_mul_u64_u64_div_u64.c b/lib/math/test_mul_u64_u64_div_u64.c
> index ea5b703cccff..f0134f25cb0d 100644
> --- a/lib/math/test_mul_u64_u64_div_u64.c
> +++ b/lib/math/test_mul_u64_u64_div_u64.c
> @@ -73,21 +73,34 @@ done
>
> */
>
> -static int __init test_init(void)
> +static u64 test_mul_u64_add_u64_div_u64(u64 a, u64 b, u64 c, u64 d);
> +
> +static int __init test_run(unsigned int fn_no, const char *fn_name)
> {
> + u64 start_time;
> int errors = 0;
> int tests = 0;
> int i;
>
> - pr_info("Starting mul_u64_u64_div_u64() test\n");
> + start_time = ktime_get_ns();
>
> for (i = 0; i < ARRAY_SIZE(test_values); i++) {
> u64 a = test_values[i].a;
> u64 b = test_values[i].b;
> u64 d = test_values[i].d;
> u64 expected_result = test_values[i].result;
> - u64 result = mul_u64_u64_div_u64(a, b, d);
> - u64 result_up = mul_u64_u64_div_u64_roundup(a, b, d);
> + u64 result, result_up;
> +
> + switch (fn_no) {
> + default:
> + result = mul_u64_u64_div_u64(a, b, d);
> + result_up = mul_u64_u64_div_u64_roundup(a, b, d);
> + break;
> + case 1:
> + result = test_mul_u64_add_u64_div_u64(a, b, 0, d);
> + result_up = test_mul_u64_add_u64_div_u64(a, b, d - 1, d);
> + break;
> + }
>
> tests += 2;
>
> @@ -106,15 +119,36 @@ static int __init test_init(void)
> }
> }
>
> - pr_info("Completed mul_u64_u64_div_u64() test, %d tests, %d errors\n",
> - tests, errors);
> - return errors ? -EINVAL : 0;
> + pr_info("Completed %s() test, %d tests, %d errors, %llu ns\n",
> + fn_name, tests, errors, ktime_get_ns() - start_time);
> + return errors;
> +}
> +
> +static int __init test_init(void)
> +{
> + pr_info("Starting mul_u64_u64_div_u64() test\n");
> + if (test_run(0, "mul_u64_u64_div_u64"))
> + return -EINVAL;
> + if (test_run(1, "test_mul_u64_u64_div_u64"))
> + return -EINVAL;
> + return 0;
> }
>
> static void __exit test_exit(void)
> {
> }
>
> +/* Compile the generic mul_u64_add_u64_div_u64() code */
> +#define div64_u64 div64_u64
> +#define div64_s64 div64_s64
> +#define iter_div_u64_rem iter_div_u64_rem
> +
> +#undef mul_u64_add_u64_div_u64
> +#define mul_u64_add_u64_div_u64 test_mul_u64_add_u64_div_u64
> +#define test_mul_u64_add_u64_div_u64 test_mul_u64_add_u64_div_u64
> +
> +#include "div64.c"
> +
> module_init(test_init);
> module_exit(test_exit);
>
> --
> 2.39.5
>
>
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