linux-kernel - Re: clock_getres() and real resolution

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Message-ID: <4F33910D.2030409@linaro.org>
Date:	Thu, 09 Feb 2012 01:25:33 -0800
From:	Dmitry Antipov <dmitry.antipov@...aro.org>
To:	Richard Cochran <richardcochran@...il.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org
Subject: Re: clock_getres() and real resolution

On 02/08/2012 09:12 PM, Richard Cochran wrote:

> I think "resolution" does not mean tick duration, but rather the finest timer unit.

#include <stdio.h>
#include <time.h>

int main (int argc, char *argv[])
{
   int i;
   struct timespec rs, ts[10];

   clock_getres (CLOCK_REALTIME, &rs);
   printf ("res: %lus %luns\n", rs.tv_sec, rs.tv_nsec);

   for (i = 0; i < 10; i++)
     clock_gettime (CLOCK_REALTIME, ts + i);
   for (i = 0; i < 10; i++)
     printf ("%d: %lus %luns\n", i, ts[i].tv_sec, ts[i].tv_nsec);

   return 0;
}

=>

res: 0s 10000000ns
0: 1328779203s 975317500ns
1: 1328779203s 975317900ns
2: 1328779203s 975318200ns
3: 1328779203s 975318400ns
4: 1328779203s 975318600ns
5: 1328779203s 975318800ns
6: 1328779203s 975319000ns
7: 1328779203s 975319300ns
8: 1328779203s 975319500ns
9: 1328779203s 975319600ns

Old Sun Fire 880, SunOS 5.10 Generic_139555-08.

100ns precision with 10ms "finest timer unit"???

Dmitry
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