linux-kernel - Re: [PATCH 10/10] sched/fair: Implement an EEVDF like policy

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Date:   Wed, 08 Mar 2023 14:36:01 +0100
From:   Mike Galbraith <efault@....de>
To:     Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
        vincent.guittot@...aro.org
Cc:     linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, corbet@....net,
        qyousef@...alina.io, chris.hyser@...cle.com,
        patrick.bellasi@...bug.net, pjt@...gle.com, pavel@....cz,
        qperret@...gle.com, tim.c.chen@...ux.intel.com, joshdon@...gle.com,
        timj@....org, kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org, joel@...lfernandes.org
Subject: Re: [PATCH 10/10] sched/fair: Implement an EEVDF like policy

On Wed, 2023-03-08 at 09:39 +0100, Mike Galbraith wrote:
>
> Curiosity got the best of me...

Remember this little bugger, allegedly distilled from a real
application control thread starvation issue?

6.3.0.g8ca09d5-master
homer:/root # time taskset -c 3 starve
expecting to receive 10000000 signals

real    0m24.424s
user    0m4.468s
sys     0m18.957s

6.3.0.g8ca09d5-eevdf
homer:/root # time taskset -c 3 starve
expecting to receive 10000000 signals
zzzzzz
^C

real    15m24.115s
user    0m3.078s
sys     0m0.000s


#include <stdlib.h>
#include <stdio.h>
#include <signal.h>
#include <unistd.h>

#include <sys/types.h>
#include <sys/wait.h>

volatile unsigned long loop;

void handler(int n)
{
	if (loop > 0)
		--loop;
}

static int child(void)
{
	pid_t ppid = getppid();

	sleep(1);
	while (1)
		kill(ppid, SIGUSR1);
	return 0;
}

int main(int argc, char **argv)
{
	pid_t child_pid;
	int r;

	loop = argc > 1 ? strtoul(argv[1], NULL, 10) : 10000000;
	printf("expecting to receive %lu signals\n", loop);

	if ((child_pid = fork()) == 0)
		exit(child());

	signal(SIGUSR1, handler);
	while (loop)
		sleep(1);
	r = kill(child_pid, SIGTERM);
	waitpid(child_pid, NULL, 0);
	return 0;
}