Re: gprof SELECT COUNT(*) results

[Qingqing Zhou <zhouqq(at)cs(dot)toronto(dot)edu>]

On Thu, 24 Nov 2005, Qingqing Zhou wrote:
>
> I may need to write some separate tests to see if this is what we should
> pay for bus lock instruction.
>

Here I come up with a test program to see how spinlock costs:

$/pgsql/src/backend/storage/lmgr#./a.out
Spinlock pair(2648542) duration: 143.134 ms
$/pgsql/src/backend/storage/lmgr#./a.out
Spinlock pair(2648542) duration: 143.107 ms
$/pgsql/src/backend/storage/lmgr#./a.out
Spinlock pair(2648542) duration: 143.104 ms

So seems lock instruction really costs ...

Regards,
Qingqing

---

/*
 * spintest.c -
 *	Test spinlock acquire/release without concurrency.
 *
 *      To compile (the -pg is to match the gprof make I used):
 *		backend/storage/lmgr#gcc -O2 -pg -Wall -I ../../../include/ spintest.c
 */

#include "postgres.h"
#include "storage/lwlock.h"
#include "storage/spin.h"
#include <sys/time.h>

#define TIMES 	2648542

int NumLocks = 0;

void
s_lock(volatile slock_t *lock, const char *file, int line)
{
	fprintf(stderr, "should never be here\n");
	abort();
}

int
main(void)
{
	int	i;
	slock_t	lock = 0;
	struct timeval start_t, stop_t;
	long usecs;

	gettimeofday(&start_t, NULL);
	for (i = 0; i < TIMES; i ++)
	{
		SpinLockAcquire_NoHoldoff(&lock);

		/* pretend to do something */
		NumLocks ++;

		SpinLockRelease_NoHoldoff(&lock);
	}
  	gettimeofday(&stop_t, NULL);


	if (stop_t.tv_usec < start_t.tv_usec)
   	{
		stop_t.tv_sec--;
		stop_t.tv_usec += 1000000;
	}

	usecs = (long) (stop_t.tv_sec - start_t.tv_sec) * 1000000
		+ (long) (stop_t.tv_usec - start_t.tv_usec);

	fprintf (stdout, "Spinlock pair(%u) duration: %ld.%03ld ms\n",
		TIMES,
		(long) ((stop_t.tv_sec - start_t.tv_sec) * 1000 +
			(stop_t.tv_usec - start_t.tv_usec) / 1000),
		(long) (stop_t.tv_usec - start_t.tv_usec) % 1000);

	return 0;
}