:
>
> Hello All,
>
> I created a very simple program which has higher priority than normal tasks and runs a tight loop. Under same test environment I ran this program on both non-rt and rt 2.6.33.5 kernel. To my suprise I see that performance of non-RT kernel is better than RT. non-RT kernel took 3 sec and 366156 usec while RT kernel took about 3 sec and 418011 usec.Can someone please explain why the performance of non-rt kernel is better than rt kernel? From the face of the test result, I feel RT has more overhead,Is there any configuration that I could do to bring down the overhead?
>
> Processor:
> ----------------
> processor : 0
> cpu : 7448
> clock : 996.000000MHz
> revision : 2.2 (pvr 8004 0202)
> bogomips : 83.10
> processor : 1
> cpu : 7448
> clock : 996.000000MHz
> revision : 2.2 (pvr 8004 0202)
> bogomips : 83.10
>
> CFS optimization:
> --------------------------
> # cat /proc/sys/kernel/sched_rt_runtime_us
> 1000000
> # cat /proc/sys/kernel/sched_rt_period_us
> 1000000
> # cat /proc/sys/kernel/sched_compat_yield
> 1
>
> Test Program:
> ---------------------
>
> main()
> {
>
> int sched_rr_min,sched_rr_max;
> struct sched_param scheduling_parameters;
> struct timeval tv,late_tv;
> suseconds_t usec_diff,avg_usec = 0;
> time_t sec_diff, avg_sec = 0;
> int i;
> long count = 1;
>
> sched_rr_min = sched_get_priority_min(SCHED_RR);
> sched_rr_max = sched_get_priority_max(SCHED_RR);
> scheduling_parameters.sched_priority = sched_rr_min+4;
> sched_setscheduler(0, SCHED_RR, &scheduling_parameters);// Run the process with the given priority
>
> for(i = 0 ; i < 150 ; i++) {
> gettimeofday(&tv, NULL);
> while(count > 0){
> //printf(".");
> count++;
> }
> gettimeofday(&late_tv, NULL);
> count = 1;
> sec_diff = (late_tv.tv_sec - tv.tv_sec);
> avg_sec += sec_diff;
> usec_diff = ( (late_tv.tv_usec > tv.tv_usec) ? (late_tv.tv_usec - tv.tv_usec) : ( tv.tv_usec - late_tv.tv_usec));
> avg_usec += usec_diff;
> printf("Iteration #%d sec %x usec %x\n",i,(sec_diff),(usec_diff));
> }
> printf("Average of #%d sec %x usec %x\n",i,(avg_sec/i),(avg_usec)/i);
> }
>
> Partial Result of non-rt kernel:
> -------------------------------------------
>
> Iteration #140 sec 3 usec 3aef8
> Iteration #141 sec 3 usec 3aefe
> Iteration #142 sec 3 usec 3aee4
> Iteration #143 sec 4 usec b935b [Why there is this periodic bump ??] [Scheduler at work??]
> Iteration #144 sec 3 usec 3aef2
> Iteration #145 sec 3 usec 3aef0
> Iteration #146 sec 3 usec 3aef4
> Iteration #147 sec 4 usec b934b
> Iteration #148 sec 3 usec 3aeed
> Iteration #149 sec 3 usec 3aef9
>
> Partial Result of rt kernel:
> -------------------------------------------
> Iteration #135 sec 3 usec 47328
> Iteration #136 sec 4 usec ac4fd
> Iteration #137 sec 3 usec 48b0b
> Iteration #138 sec 3 usec 4738c
> Iteration #139 sec 4 usec ac4d5
> Iteration #140 sec 3 usec 483cb
> Iteration #141 sec 3 usec 48500
> Iteration #142 sec 4 usec acc49
> Iteration #143 sec 3 usec 47c1f
> Iteration #144 sec 3 usec 478c2
> Iteration #145 sec 3 usec 47e48
> Iteration #146 sec 4 usec ac9b5
> Iteration #147 sec 3 usec 48de4
> Iteration #148 sec 3 usec 46fbe
> Iteration #149 sec 4 usec ac52e
> Average of #150 sec 3 usec 660db
>
> Thanks,
> Mani
>
>
>
>
--
Thanks,
Manik
Think twice about a tree before you take a printout
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