Soft realtime

Recently we wanted to try out some hard real time stuff. When we attempted it, the results were not satisfactory. Today, I just tried a program to see how a soft real time program performs against a normal program.
(Notice the use of SCHED_FIFO and a priority

#include <stdio.h> #include <sched.h> #include <sys/time.h> int main() { int retval=-1; struct sched_param sp; struct timeval tv; int old=0; #if defined(SFT_RLT) sp.sched_priority=20; retval=sched_setscheduler(0,SCHED_FIFO,&sp); printf("Ret= %d\n",retval); #endif while(1) { gettimeofday(&tv,NULL); old=(tv.tv_usec-old)<0?1000*1000+tv.tv_usec-old:tv.tv_usec-old; printf("%u %u %u \n",tv.tv_sec, tv.tv_usec,old); old=tv.tv_usec; usleep(1000*200); } return 0; }

I compiled two binaries from this

gcc -DSFT_RLT rt.c -o rt
gcc rt.c -o nrt

As one can easily see, the first one is a soft realtime program and the second is a normal program. I ran these programs under two scenarios. One, when the system was relatively free; two, when the system was loaded. This is what I did and observed.

Normal scenario (X, FVWM, Terminal, bittorrent and Firefox)

./rt	./nrt
1246142672 137029 200069 1246142672 337101 200072 1246142672 537171 200070 1246142672 737242 200071 1246142672 937312 200070 1246142673 137344 200032 1246142673 337413 200069 1246142673 537486 200073 1246142673 737557 200071 1246142673 937627 200070	1246142672 004983 200072 1246142672 205055 200072 1246142672 405127 200072 1246142672 605199 200072 1246142672 805265 200066 1246142673 005331 200066 1246142673 205402 200071 1246142673 405538 200136 1246142673 605604 200066 1246142673 805668 200064

Then I tried running the same under loaded condition. (Just played a movie using mplayer. The other processes which were earlier running were running now also)

./rt	./nrt
1246146025 832916 200046 1246146026 032951 200035 1246146026 233010 200059 1246146026 433064 200054 1246146026 633097 200033 1246146026 833150 200053 1246146027 033203 200053 1246146027 233255 200052 1246146027 433286 200031 1246146027 633317 200031 1246146027 833368 200051	1246146025 803540 200145 1246146026 003647 200107 1246146026 203734 200087 1246146026 403823 200089 1246146026 603918 200095 1246146026 804006 200088 1246146027 004127 200121 1246146027 204204 200077 1246146027 404257 200053 1246146027 604314 200057 1246146027 804368 200054

I guess the difference in result is noticeable.This is easier to achieve compared to hard rt, since there is no kernel patches needed. When we make a break through with hard rt, I will post again