Very Computer

Hi

I've a strange behavior using fwrite.
My program writes 5 MB on the disk with buffer of 50000 bytes, but
sometime a single fwrite waits for more than 1 seconds.

System features :
- reiserfs
- DMA actived.

This is the code I used to test fwrite

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

const __int64 TIME_T_ZERO_TIME  = 116444700000000000;  

longlong UTime64()
{
  struct timeval tv;
  struct timezone tz;
  gettimeofday(&tv,&tz);

  long long Ret = (__int64)tv.tv_sec*10000000+TIME_T_ZERO_TIME+(__int64)tv.tv_usec*10
+ (__int64)36000000000;

Quote:}

int main(int argc, char** argv)
{
  char buffer[100000];
  int size;
  __int64 tTime1;

  int Count = 0;
  char Name[2014];
  while (1)
  {
    sprintf(Name,"/tmp/prova_fwrite_%d.tmp",Count++);
    FILE* f = fopen(Name,"w");

    int Size = 50000;
    int SizeWritten = 0;

    while (SizeWritten < 5000000)
    {
      tTime1 = UTime64();
      size = fwrite(buffer,1,Size,f);
      tTime2 = UTime64();

      float fl = (float)(tTime2-tTime1) / size;
      if (fl>50 && tTime2-tTime1 > 10000000) // > 1 sec
      {
        printf("Ratio = %f - %d - %llu\n",fl,size,tTime2-tTime1);
      }

      SizeWritten[i] += size;
    }

    fclose(f);

    usleep(1000);
  }

  return 1;

Quote:}

And this is the output
(idx)    (delta T / size)     (size) (delta T sec)

15730 - Ratio2 = 305.085602 - 50000 - 1,5254330
19665 - Ratio2 = 559.221008 - 50000 - 2,7961100
23154 - Ratio2 = 490.265991 - 50000 - 2,4513350
24989 - Ratio2 = 430.956207 - 50000 - 2,1547860
27135 - Ratio2 = 283.720795 - 50000 - 1,4186090
31161 - Ratio2 = 238.803802 - 50000 - 1,1940240
42781 - Ratio2 = 263.786591 - 50000 - 1,3189380
....