linux-kernel - Re: [PATCH v2 2/2] mul_u64_u64_div

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Message-ID: <dzohdvfrh3jivw5mt7aepxezzrvq422xptx5zyz4mouxypnt5v@hj75gj622i6x>
Date: Thu, 4 Jul 2024 18:42:09 +0200
From: Uwe Kleine-König <u.kleine-koenig@...libre.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Nicolas Pitre <nico@...xnic.net>, linux-kernel@...r.kernel.org, 
	Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH v2 2/2] mul_u64_u64_div_u64: basic sanity test

Hello,

On Wed, Jul 03, 2024 at 11:36:31PM +0200, Uwe Kleine-König wrote:
> I intend to do a performance test of Nico's code. I hope I get to that
> tomorrow.

I'm really surprised, I expected a penalty for being more correct, but
there doesn't seem to be one.

I tested on an stm32mp135f SoC (i.e. armv7) with:

	time pwmtestperf -p 3 -P 1000000000 -S 1000

which configures the PWM 1000001 times, each configuration calls
mul_u64_u64_div_u64() three times. And I got

	real    0m 37.17s
	user    0m 0.69s
	sys     0m 36.40s

on 6.10.0-rc1 (+ various pwm related patches) and

	real	0m 36.93s
	user	0m 0.58s
	sys	0m 36.26s

with Nico's patch applied on top.

Looking at the patch in detail, I always hit ilog2(a) + ilog2(b) <= 62,
so on 2nd thought it's not surprising that the performance is similar.

Tested-by: Uwe Kleine-König <u.kleine-koenig@...libre.com>

Thanks!
Uwe

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