#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
int main()
{
char c;
int in;
int i;
in = open("in.txt", O_RDONLY);
for(i=0; i<1000000; i++){
read(in,&c,1);
}
return 0;
}
#dd if=/dev/zero of=in.txt bs=1M count=1
#gcc main.c -o main
#time ./main
real 0m0.258s
user 0m0.030s
sys 0m0.227s
# gcc main.c -o main
# perf stat ./main
Performance counter stats for './main':
251.508810 task-clock # 0.997 CPUs utilized
1 context-switches # 0.000 M/sec
1 CPU-migrations # 0.000 M/sec
97 page-faults # 0.000 M/sec
600,644,444 cycles # 2.388 GHz [83.38%]
122,000,095 stalled-cycles-frontend # 20.31% frontend cycles idle [83.33%]
45,707,976 stalled-cycles-backend # 7.61% backend cycles idle [66.66%]
1,008,492,870 instructions # 1.68 insns per cycle
# 0.12 stalled cycles per insn [83.33%]
177,244,889 branches # 704.726 M/sec [83.32%]
7,583 branch-misses # 0.00% of all branches [83.33%]
$ vmstat 1
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
r b swpd free buff cache si so bi bo in cs us sy id wa st
1 0 0 1231716 339244 55474204 0 0 6 496 0 0 7 3 90 0 0
2 0 0 1231352 339244 55474204 0 0 0 128 57402 24593 5 2 92 0 0
2 0 0 1230988 339244 55474528 0 0 0 140 55267 24213 5 2 93 0 0
2 0 0 1230988 339244 55474528 0 0 0 332 56328 23672 5 2 93 0 0
# strace -c php main.php
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
97.24 0.039698 1 30003 poll
2.20 0.000899 0 10003 sendto
0.30 0.000122 0 10000 recvfrom
0.13 0.000053 0 10069 gettimeofday
0.03 0.000013 2 6 socket
0.03 0.000012 0 408 munmap
0.02 0.000008 0 657 read
# grep ctxt /proc/14862/status
voluntary_ctxt_switches: 4
nonvoluntary_ctxt_switches: 43
# grep ctxt /proc/14862/status
voluntary_ctxt_switches: 10005
nonvoluntary_ctxt_switches: 49
# php main.php
# cat /proc/softirqs
CPU0 CPU1 CPU2 CPU3
HI: 0 0 0 0
TIMER: 196173081 145428444 154228333 163317242
NET_TX: 0 0 0 0
NET_RX: 178159928 116073 10108 160712
# cat /proc/softirqs
CPU0 CPU1 CPU2 CPU3
HI: 0 0 0 0
TIMER: 196173688 145428634 154228610 163317624
NET_TX: 0 0 0 0
NET_RX: 178170212 116073 10108 160712
-------------------------------------------------------------------------
Host OS 2p/0K 2p/16K 2p/64K 8p/16K 8p/64K 16p/16K 16p/64K
ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw
--------- ------------- ------ ------ ------ ------ ------ ------- -------
bjzw_46_7 Linux 2.6.32- 2.7800 2.7800 2.7000 4.3800 4.0400 4.75000 5.48000
