系统调用开销测试

#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