Let me demonstrate a benefit of VIRT_CPU_ACCOUNTING. Here is a sample program: ------------------------------------------------- #include <stdio.h> #include <unistd.h> /* 300 million */ #define LOOP 300000000 int main(int argc, char **argv) { unsigned long sum = 0; int i; int c = argc > 1 ? atoi(argv[1]) : LOOP; printf("sum up 1 to %d: usleep(0) every %d\n", LOOP, c); for (i = 1; i <= LOOP; i++) { sum += i; if (!(i % c)) usleep(0); } printf("sleep %d times: sum = %ld\n", LOOP/c, sum); } ------------------------------------------------- If I make and execute this one, ... ------------------------------------------------- [root@xxxxxx ~]# time ./a.out sum up 1 to 300000000: usleep(0) every 300000000 sleep 1 times: sum = 45000000150000000 real 0m11.850s user 0m11.847s sys 0m0.002s ------------------------------------------------- millions loop take about 12 sec on my system. Then, let insert some pause in the loop by usleep(0) ... ------------------------------------------------- # pause every 1 million [root@xxxxxx ~]# time ./a.out 1000000 sum up 1 to 300000000: usleep(0) every 1000000 sleep 300 times: sum = 45000000150000000 real 0m12.089s user 0m11.701s # nothing peculiar sys 0m0.001s ------------------------------------------------- # pause every 100 thousands [root@xxxxxx ~]# time ./a.out 100000 sum up 1 to 300000000: usleep(0) every 100000 sleep 3000 times: sum = 45000000150000000 real 0m15.002s user 0m9.001s # new record! sys 0m0.003s ------------------------------------------------- # pause every 50 thousands [root@xxxxxx ~]# time ./a.out 50000 sum up 1 to 300000000: usleep(0) every 50000 sleep 6000 times: sum = 45000000150000000 real 0m18.421s user 0m6.002s # finished in the half! sys 0m0.002s ------------------------------------------------- # pause every 10 thousands [root@xxxxxx ~]# time ./a.out 10000 sum up 1 to 300000000: usleep(0) every 10000 sleep 30000 times: sum = 45000000150000000 real 0m34.977s user 0m0.000s # done without cpu! sys 0m0.002s ------------------------------------------------- What a terrible paranormal phenomena? Of course this is an intentional misuse of tick-sampling based time accounting. So if you repeat yielding the cpu before a timer interrupt, and getting back the cpu after the interrupt, you can steal cpu time without being noticed by anyone. However, once this accurate cpu time accounting, produced by my patches, are enabled: ------------------------------------------------- [root@23new ~]# time ./a.out 1000000 sum up 1 to 300000000: usleep(0) every 1000000 sleep 300 times: sum = 45000000150000000 real 0m12.308s user 0m11.803s sys 0m0.048s ------------------------------------------------- [root@23new ~]# time ./a.out 100000 sum up 1 to 300000000: usleep(0) every 100000 sleep 3000 times: sum = 45000000150000000 real 0m15.002s user 0m11.803s sys 0m0.064s ------------------------------------------------- [root@23new ~]# time ./a.out 50000 sum up 1 to 300000000: usleep(0) every 50000 sleep 6000 times: sum = 45000000150000000 real 0m18.004s user 0m11.803s sys 0m0.071s ------------------------------------------------- [root@23new ~]# time ./a.out 10000 sum up 1 to 300000000: usleep(0) every 10000 sleep 30000 times: sum = 45000000150000000 real 0m36.497s user 0m11.808s sys 0m0.139s ------------------------------------------------- you cannot be time-thief anymore. Thanks, H.Seto - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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