linux-kernel - Re: [ISSUE] sched/cgroup: Does cpu-cgroup still works fine nowadays?

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Date:	Wed, 14 May 2014 15:36:50 +0800
From:	Michael wang <wangyun@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
	Alex Shi <alex.shi@...aro.org>, Paul Turner <pjt@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [ISSUE] sched/cgroup: Does cpu-cgroup still works fine nowadays?

Hi, Peter

On 05/13/2014 10:23 PM, Peter Zijlstra wrote:
[snip]
> 
> I you want to investigate !spinners, replace the ABC with slightly more
> complex loads like: https://lkml.org/lkml/2012/6/18/212

I've done a little reform, enabled multi-threads and add a mutex,
please check the code below for details.

I built it by:
	gcc -o my_tool cgroup_tool.c -lpthread

distro mount cpu-subsys under '/sys/fs/cgroup/cpu', create group like:
	mkdir /sys/fs/cgroup/cpu/A
	mkdir /sys/fs/cgroup/cpu/B
	mkdir /sys/fs/cgroup/cpu/C

and then:
	echo $$ > /sys/fs/cgroup/cpu/A/tasks ; ./my_tool -l
	echo $$ > /sys/fs/cgroup/cpu/B/tasks ; ./my_tool -l
	echo $$ > /sys/fs/cgroup/cpu/C/tasks ; ./my_tool 50

the results in top is around:

		A	B	C
	CPU%	550	550	100

While only './my_tool 50' was running, it require around 300%.

And this could also be reproduced by dbench, stress combination like:
	echo $$ > /sys/fs/cgroup/cpu/A/tasks ; dbench 6
	echo $$ > /sys/fs/cgroup/cpu/B/tasks ; stress -c 6
	echo $$ > /sys/fs/cgroup/cpu/C/tasks ; stress -c 6

Now it seems more like a generic problem... will keep investigating, please
let me know if there are any suggestions :)

Regards,
Michael Wang



#include <sys/time.h>
#include <unistd.h>
#include <stdio.h>
#include <pthread.h>

pthread_mutex_t my_mutex;

unsigned long long stamp(void)
{
	struct timeval tv;
	gettimeofday(&tv, NULL);

	return (unsigned long long)tv.tv_sec * 1000000 + tv.tv_usec;
}
void consume(int spin, int total)
{
	unsigned long long begin, now;
	begin = stamp();

	for (;;) {
		pthread_mutex_lock(&my_mutex);
		now = stamp();
		if ((long long)(now - begin) > spin) {
			pthread_mutex_unlock(&my_mutex);
			usleep(total - spin);
			pthread_mutex_lock(&my_mutex);
			begin += total;
		}
		pthread_mutex_unlock(&my_mutex);
	}
}

struct my_data {
	int spin;
	int total;
};

void *my_fn_sleepy(void *arg)
{
	struct my_data *data = (struct my_data *)arg;
	consume(data->spin, data->total);
	return NULL;
}

void *my_fn_loop(void *arg)
{
	while (1) {};
	return NULL;
}

int main(int argc, char **argv)
{
	int period = 100000; /* 100ms */
	int frac;
	struct my_data data;
	pthread_t last_thread;
	int thread_num = sysconf(_SC_NPROCESSORS_ONLN) / 2;
	void *(*my_fn)(void *arg) = &my_fn_sleepy;

	if (thread_num <= 0 || thread_num > 1024) {
		fprintf(stderr, "insane processor(half) size %d\n", thread_num);
		return -1;
	}

	if (argc == 2 && !strcmp(argv[1], "-l")) {
		my_fn = &my_fn_loop;
		printf("loop mode enabled\n");
		goto loop_mode;
	}

	if (argc < 2) {
		fprintf(stderr, "%s <frac> [<period>]\n"
				"  frac   -- [1-100] %% of time to burn\n"
				"  period -- [usec] period of burn/sleep cycle\n",
				argv[0]);
		return -1;
	}

	frac = atoi(argv[1]);
	if (argc > 2)
		period = atoi(argv[2]);
	if (frac > 100)
		frac = 100;
	if (frac < 1)
		frac = 1;

	data.spin = (period * frac) / 100;
	data.total = period;

loop_mode:
	pthread_mutex_init(&my_mutex, NULL);
	while (thread_num--) {
		if (pthread_create(&last_thread, NULL, my_fn, &data)) {
			fprintf(stderr, "Create thread failed\n");
			return -1;
		}
	}

	printf("Threads never stop, CTRL + C to terminate\n");

	pthread_join(last_thread, NULL);
	pthread_mutex_destroy(&my_mutex);	//won't happen
	return 0;
}

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View attachment "cgroup_tool.c" of type "text/x-csrc" (2043 bytes)