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On Tue, 4 Nov 2003 15:18:00 +0200, Gilad Ben-Yossef <[EMAIL PROTECTED]> wrote:
>
> On Tuesday 04 November 2003 14:43, Ehud Karni wrote:
>
> > I tested the select call on various machines.
> > 1. It is not accurate enough (2 ms deviations).
>
> Yes it does, you don't seem to use sched_setscheduler in your test program to
> give your proccess real time priority. setpriority only changes the nice
> level of the proccess. If you want real time guantees (which you do here) you
> need to ask the kernel to subject your proccess to real time scheduling.
See test results below.
> > 2. It can not be used for delays < 10 ms.
>
> Unless you recompile the kernel, you are correct.
I enhanced my test program by adding the scheduler priority like this:
#include <sched.h>
struct sched_param scd_prm ;
scd_prm.sched_priority = 10 ; /* anything greater than 0 */
sched_setscheduler ( 0 , SCHED_RR , & scd_prm ) ; /* try to set scheduler
policy and priority */
setpriority ( PRIO_PROCESS , 0 , atoi ( argv [ 2 ] ) ) ;/* set nice priority (no
check) */
fprintf ( stderr , "Run at %d sched priority, %d nice " ,
sched_getscheduler ( 0 ) , /* get schedule priority */
getpriority ( PRIO_PROCESS , 0 ) ) ; /* get process priority */
I tested the select sleep and my conclusions are:
1. Even with Real time priority it is accurate to within 0.1 mill
seconds (see 1st set of results).
2. The granularity is 10 ms even for times > 10 ms.
Here are some of the results:
Run at 2 sched priority, -20 nice sleeped 37076 usec * 100 times, Elapsed 3995 msecs
Run at 2 sched priority, -20 nice sleeped 37076 usec * 100 times, Elapsed 3995 msecs
Run at 2 sched priority, -20 nice sleeped 37076 usec * 100 times, Elapsed 3998 msecs
Run at 2 sched priority, -20 nice sleeped 37076 usec * 100 times, Elapsed 4000 msecs
Run at 2 sched priority, -20 nice sleeped 37076 usec * 100 times, Elapsed 3992 msecs
Run at 2 sched priority, -20 nice sleeped 37076 usec * 100 times, Elapsed 3993 msecs
Run at 2 sched priority, -20 nice sleeped 37076 usec * 100 times, Elapsed 3995 msecs
Run at 2 sched priority, -20 nice sleeped 1 usec * 100 times, Elapsed 997 msecs
Run at 2 sched priority, -20 nice sleeped 38 usec * 100 times, Elapsed 991 msecs
Run at 2 sched priority, -20 nice sleeped 987 usec * 100 times, Elapsed 1000 msecs
Run at 2 sched priority, -20 nice sleeped 1987 usec * 100 times, Elapsed 992 msecs
Run at 2 sched priority, -20 nice sleeped 9876 usec * 100 times, Elapsed 1000 msecs
Run at 2 sched priority, -20 nice sleeped 19876 usec * 100 times, Elapsed 1997 msecs
Run at 2 sched priority, -20 nice sleeped 18076 usec * 100 times, Elapsed 1995 msecs
Run at 2 sched priority, -20 nice sleeped 19076 usec * 100 times, Elapsed 1991 msecs
Run at 2 sched priority, -20 nice sleeped 37076 usec * 100 times, Elapsed 3999 msecs
Run at 2 sched priority, -20 nice sleeped 36076 usec * 100 times, Elapsed 3994 msecs
Run at 2 sched priority, -20 nice sleeped 35076 usec * 100 times, Elapsed 3993 msecs
Run at 2 sched priority, -20 nice sleeped 34076 usec * 100 times, Elapsed 3998 msecs
Run at 2 sched priority, -20 nice sleeped 33076 usec * 100 times, Elapsed 3997 msecs
Run at 2 sched priority, -20 nice sleeped 32076 usec * 100 times, Elapsed 3993 msecs
Run at 2 sched priority, -20 nice sleeped 31076 usec * 100 times, Elapsed 3993 msecs
Run at 2 sched priority, -20 nice sleeped 30076 usec * 100 times, Elapsed 3993 msecs
Run at 2 sched priority, -20 nice sleeped 29076 usec * 100 times, Elapsed 2998 msecs
Run at 2 sched priority, -20 nice sleeped 29976 usec * 100 times, Elapsed 2994 msecs
Ehud.
- --
Ehud Karni Tel: +972-3-7966-561 /"\
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