linux-kernel - Re: [PATCH] sched/fair: Remove max_vruntime() and min

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Message-ID: <Y1o5i1Trk2aRZY4q@hirez.programming.kicks-ass.net>
Date:   Thu, 27 Oct 2022 09:55:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yajun Deng <yajun.deng@...ux.dev>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Remove max_vruntime() and min_vruntime()

On Thu, Oct 27, 2022 at 09:54:09AM +0200, Peter Zijlstra wrote:
> On Thu, Oct 27, 2022 at 09:53:51AM +0800, Yajun Deng wrote:
> > There is no need to write max_vruntime() and min_vruntime() functions,
> > we can use max_t() and min_t() instead.
> 
> Here; I did your homework for you:
> 
> /* max.c */
> #include <stdio.h>
> #include <stdint.h>
> #include <stdlib.h>
> 
> typedef unsigned long long u64;
> typedef unsigned long long s64;

This should obviously be just 'long long', but the result doesn't
change.

/me goes goes get more wake-up juice.

> 
> static u64 max_vruntime(u64 max_vruntime, u64 vruntime)
> {
> 	s64 delta = (s64)(vruntime - max_vruntime);
> 	if (delta > 0)
> 		max_vruntime = vruntime;
> 	return max_vruntime;
> }
> 
> static u64 max(u64 a, u64 b)
> {
> 	return a > b ? a : b;
> }
> 
> int main(int argc, char **argv)
> {
> 	u64 a, b;
> 
> 	if (argc < 3)
> 		return 0;
> 
> 	a = strtoll(argv[1], NULL, 10);
> 	b = strtoll(argv[2], NULL, 10);
> 	printf("         max(%lu, %lu) = %lu\n", a, b, max(a,b));
> 	printf("max_vruntime(%lu, %lu) = %lu\n", a, b, max_vruntime(a,b));
> 
> 	return 0;
> }
> 
> $ ./max -1 0
>          max(18446744073709551615, 0) = 18446744073709551615
> max_vruntime(18446744073709551615, 0) = 0