Re: [PATCH 6/9] clockpro-clockpro.patch

[IWAMOTO Toshihiro <iwamoto@valinux.co.jp>]

(Removed linux-kernel@ from Cc:)

At Tue, 24 Jan 2006 15:30:10 +0900,
IWAMOTO Toshihiro wrote:
> I thought this situation means that page access frequencies cannot be
> correctly compared and leads to suboptimal performance, but I couldn't
> prove that.  However, I've managed to create an example workload where
> clockpro performs worse.  I'm not sure if the example is related to
> this hand problem.  I'll describe it in the next mail.

Environment: Dell 1850 4GB EM64T CPUx2 HT disabled, x86_64 kernel
Kernel 1: linux-2.6.15-rc5
Kernel 2: linux-2.6.15-rc5 + clockpro patch posted in 2005/12/31
Kernel 3: linux-2.6.15-rc5 + clockpro patch posted in 2005/12/31 +
	  modification to disable page cache usage from ZONE_DMA
	  (to rule out possible zone balancing related problem)
Kernel 1 and 2 were booted with "mem=1008m", Kernel 3 was booted with
"mem=1024m".

The test program: 2read.c (attached below)
	2read.c repeatedly reads from two files zero and zero2.
	Command line arguments specify the ranges to be read. (See the
	code for detail)
	It prints the number of read operations/2 every 5 seconds and
	terminates in 5 minutes.

$ cc -O 2read.c
$ ls -l zero*
-rw-r--r--  1 toshii users 1073741824 2006-01-13 17:27 zero
-rw-r--r--  1 toshii users 1572864000 2006-01-20 18:20 zero2

(with Kernel 1)
$ for n in 100 200 300 400 500; do
> ./a.out -n $n $((1100-$n)) > /tmp/2d.$n ; done
(with Kernel 2)
$ for n in 100 200 300 400 500; do
> ./a.out -n $n $((1100-$n)) > /tmp/2d.c.$n ; done
(with Kernel 3)
$ for n in 100 200 300 400 500; do
> ./a.out -n $n $((1100-$n)) > /tmp/2d.c.nodma.$n ; done

The table below is the last numbers printed by the test program
((number of reads)/2 in 5 minutes).  Clockpro (with or without the
ZONE_DMA modification) is always slower with one exception, and
the slowdown can be as large as 42-54%.

I've put the complete data and some generated figures at
http://people.valinux.co.jp/~iwamoto/clockpro-20051231/

 n     Kernel 1    Kernel 2   Kernel 3
======================================
100    373600      298720     395818
200    385639	   272749     272166
300    371047	   243734     262370
400    367691	   213974     169714
500    147130	   126284     103038

$ cat 2read.c
#include <fcntl.h>
#include <signal.h>
#include <time.h>
#include <sys/time.h>
#include <stdlib.h>
#include <unistd.h>

#define BLKSZ	65536

unsigned int nread = 0;
void alrmhand(int);

int main(int argc, char **argv)
{
	int fd1, fd2, n;
	off_t size1, size2, p1 = 0, p2 = 0;
	struct itimerval it;
	time_t tm, dummy;
	char buf[BLKSZ];

	if (argc < 3)
		exit(EXIT_FAILURE);

	size1 = atoi(argv[1]);
	size1 *= 1024 * 1024;
	size2 = atoi(argv[2]);
	size2 *= 1024 * 1024;

	fd1 = open("zero", O_RDONLY);
	fd2 = open("zero2", O_RDONLY);
	if (fd1 < 0 || fd2 < 0) {
		perror("open");
		exit(EXIT_FAILURE);
	}

	/* XXX check filesize */

	memset(&it, 0, sizeof(it));
	it.it_interval.tv_sec = 5;
	it.it_value.tv_sec = 5;
	signal(SIGALRM, alrmhand);
	setitimer(ITIMER_REAL, &it, NULL);
	tm = time(&dummy) + 300;

	while (1) {
		n = read(fd1, buf, BLKSZ);
		if (n != BLKSZ) {
			perror("read");
			exit(EXIT_FAILURE);
		}
		n = read(fd2, buf, BLKSZ);
		if (n != BLKSZ) {
			perror("read");
			exit(EXIT_FAILURE);
		}
		p1 += BLKSZ;
		p2 += BLKSZ;
		if (p1 > size1) {
			p1 = 0;
			if (lseek(fd1, 0, SEEK_SET) < 0) {
				perror("lseek");
				exit(EXIT_FAILURE);
			}
		}
		if (p2 > size2) {
			p2 = 0;
			if (lseek(fd2, 0, SEEK_SET) < 0) {
				perror("lseek");
				exit(EXIT_FAILURE);
			}
		}
		nread++;
		if (tm < time(&dummy))
			exit(0);
	}
}


void
alrmhand(int i)
{

	printf("%u\n", nread);
}

--
IWAMOTO Toshihiro

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