linux-kernel - Re: [patch 0/3] [Announcement] Performance Counters for Linux

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Date:	Fri, 5 Dec 2008 08:03:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephane Eranian <eranian@...glemail.com>,
	Eric Dumazet <dada1@...mosbay.com>,
	Robert Richter <robert.richter@....com>,
	Arjan van de Veen <arjan@...radead.org>,
	Peter Anvin <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [patch 0/3] [Announcement] Performance Counters for Linux


* Ingo Molnar <mingo@...e.hu> wrote:

> This can be done in a very natural way with our abstraction, and the 
> "hello.c" example happens to do exactly that:

multiple people pointed out that we have not posted hello.c :-/

Here's a simple standalone example (full working code attached below):

int main(void)
{
	unsigned long long count1, count2;
	int fd1, fd2, ret;

	fd1 = perf_counter_open(PERF_COUNT_INSTRUCTIONS, 0, 0, 0, -1);
	assert(fd1 >= 0);
	fd2 = perf_counter_open(PERF_COUNT_CACHE_MISSES, 0, 0, 0, -1);
	assert(fd1 >= 0);

	for (;;) {
		ret = read(fd1, &count1, sizeof(count1));
		assert(ret == 8);
		ret = read(fd2, &count2, sizeof(count2));
		assert(ret == 8);

		printf("counter1 value: %Ld instructions\n", count1);
		printf("counter2 value: %Ld cachemisses\n",  count2);
		sleep(1);
	}
	return 0;
}


which gives this output (one readout per second):

  titan:~/perf-counter-test> ./simple 
  counter1 value: 0 instructions
  counter2 value: 0 cachemisses
  counter1 value: 23 instructions
  counter2 value: 0 cachemisses
  counter1 value: 2853 instructions
  counter2 value: 6 cachemisses
  counter1 value: 5736 instructions
  counter2 value: 7 cachemisses
  counter1 value: 8619 instructions
  counter2 value: 8 cachemisses
  counter1 value: 11502 instructions
  counter2 value: 8 cachemisses
  ^C

You need our patchset but then the code below will work just fine. No 
libraries, no context setup, nothing - just what is more interesting: the 
counter and profiling data.

	Ingo

----------------->
/*
 * Very simple performance counter testcase.
 */
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/uio.h>

#include <linux/unistd.h>

#include <assert.h>
#include <unistd.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <fcntl.h>

#ifdef __x86_64__
# define __NR_perf_counter_open	295
#endif

#ifdef __i386__
# define __NR_perf_counter_open 333
#endif

int
perf_counter_open(int		hw_event_type,
                  unsigned int	hw_event_period,
                  unsigned int	record_type,
                  pid_t		pid,
                  int		cpu)
{
	return syscall(__NR_perf_counter_open, hw_event_type, hw_event_period,
			record_type, pid, cpu);
}

enum hw_event_types {
	PERF_COUNT_CYCLES,
	PERF_COUNT_INSTRUCTIONS,
	PERF_COUNT_CACHE_REFERENCES,
	PERF_COUNT_CACHE_MISSES,
	PERF_COUNT_BRANCH_INSTRUCTIONS,
	PERF_COUNT_BRANCH_MISSES,
};

int main(void)
{
	unsigned long long count1, count2;
	int fd1, fd2, ret;

	fd1 = perf_counter_open(PERF_COUNT_INSTRUCTIONS, 0, 0, 0, -1);
	assert(fd1 >= 0);
	fd2 = perf_counter_open(PERF_COUNT_CACHE_MISSES, 0, 0, 0, -1);
	assert(fd1 >= 0);

	for (;;) {
		ret = read(fd1, &count1, sizeof(count1));
		assert(ret == 8);
		ret = read(fd2, &count2, sizeof(count2));
		assert(ret == 8);

		printf("counter1 value: %Ld instructions\n", count1);
		printf("counter2 value: %Ld cachemisses\n",  count2);
		sleep(1);
	}
	return 0;
}

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