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From: Andrew Morton <akpm@linux-foundation.org>
To: David Laight <david.laight.linux@gmail.com>
Cc: linux-kernel@vger.kernel.org, u.kleine-koenig@baylibre.com,
	Nicolas Pitre <npitre@baylibre.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Biju Das <biju.das.jz@bp.renesas.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Li RongQing <lirongqing@baidu.com>, Yu Kuai <yukuai3@huawei.com>,
	Khazhismel Kumykov <khazhy@chromium.org>,
	Jens Axboe <axboe@kernel.dk>,
	x86@kernel.org
Subject: Re: [PATCH v4 next 0/9] Implement mul_u64_u64_div_u64_roundup()
Date: Thu, 30 Oct 2025 21:29:24 -0700	[thread overview]
Message-ID: <20251030212924.35d15008efe63256762a294b@linux-foundation.org> (raw)
In-Reply-To: <20251029173828.3682-1-david.laight.linux@gmail.com>

On Wed, 29 Oct 2025 17:38:19 +0000 David Laight <david.laight.linux@gmail.com> wrote:

> The pwm-stm32.c code wants a 'rounding up' version of mul_u64_u64_div_u64().
> This can be done simply by adding 'divisor - 1' to the 128bit product.
> Implement mul_u64_add_u64_div_u64(a, b, c, d) = (a * b + c)/d based on the
> existing code.
> Define mul_u64_u64_div_u64(a, b, d) as mul_u64_add_u64_div_u64(a, b, 0, d) and
> mul_u64_u64_div_u64_roundup(a, b, d) as mul_u64_add_u64_div_u64(a, b, d-1, d).
> 
> Only x86-64 has an optimsed (asm) version of the function.
> That is optimised to avoid the 'add c' when c is known to be zero.
> In all other cases the extra code will be noise compared to the software
> divide code.
> 
> The test module has been updated to test mul_u64_u64_div_u64_roundup() and
> also enhanced it to verify the C division code on x86-64 and the 32bit
> division code on 64bit.

Thanks, I added this to mm.git's mm-nonmm-unstable branch for some
linux-next exposure.  I have a note that [3/9] may be updated in
response to Nicolas's comment.



  parent reply	other threads:[~2025-10-31  4:29 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-10-29 17:38 David Laight
2025-10-29 17:38 ` [PATCH v4 next 1/9] lib: mul_u64_u64_div_u64() rename parameter 'c' to 'd' David Laight
2025-10-29 17:38 ` [PATCH v4 next 2/9] lib: mul_u64_u64_div_u64() Combine overflow and divide by zero checks David Laight
2025-10-29 18:02   ` Nicolas Pitre
2025-10-29 17:38 ` [PATCH v4 next 3/9] lib: mul_u64_u64_div_u64() simplify check for a 64bit product David Laight
2025-10-29 18:11   ` Nicolas Pitre
2025-10-31  9:19     ` David Laight
2025-10-31 17:26       ` Nicolas Pitre
2025-10-31 18:04         ` David Laight
2025-10-31 18:45           ` Nicolas Pitre
2025-10-31 20:12             ` David Laight
2025-10-29 17:38 ` [PATCH v4 next 4/9] lib: Add mul_u64_add_u64_div_u64() and mul_u64_u64_div_u64_roundup() David Laight
2025-10-29 18:17   ` Nicolas Pitre
2025-10-31 20:59   ` David Laight
2025-11-01  2:12     ` Andrew Morton
2025-10-29 17:38 ` [PATCH v4 next 5/9] lib: Add tests for mul_u64_u64_div_u64_roundup() David Laight
2025-10-29 18:26   ` Nicolas Pitre
2025-10-29 17:38 ` [PATCH v4 next 6/9] lib: test_mul_u64_u64_div_u64: Test both generic and arch versions David Laight
2025-10-29 18:53   ` Nicolas Pitre
2025-11-01 19:35   ` kernel test robot
2025-11-01 20:59   ` kernel test robot
2025-11-02 10:36     ` David Laight
2025-10-29 17:38 ` [PATCH v4 next 7/9] lib: mul_u64_u64_div_u64() optimise multiply on 32bit x86 David Laight
2025-10-29 19:01   ` Nicolas Pitre
2025-10-29 17:38 ` [PATCH v4 next 8/9] lib: mul_u64_u64_div_u64() Optimise the divide code David Laight
2025-10-29 20:47   ` Nicolas Pitre
2025-10-29 17:38 ` [PATCH v4 next 9/9] lib: test_mul_u64_u64_div_u64: Test the 32bit code on 64bit David Laight
2025-10-29 20:48   ` Nicolas Pitre
2025-10-31  4:29 ` Andrew Morton [this message]
2025-11-04 17:16   ` [PATCH v4 next 0/9] Implement mul_u64_u64_div_u64_roundup() Nicolas Pitre
2025-10-31 13:52 ` Oleg Nesterov
2025-10-31 16:17   ` David Laight

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