The following code was compiled with VisualAge C++ and run through the
profiler.  No calls to DosSubSet were traced.  DosWrite consumed 99%
of runtime, DosClose 1%, DosOpen was the only other function traced.

#define INCL_DOS

#include 
#include 

static char buf[30000];

int main(void) {

  int   x;
  HFILE fq;
  ULONG action;
  ULONG newsize = 0;
  ULONG fileAttr = 0;
  ULONG openAction = 0;
  ULONG openMode = 0;
  ULONG actualWritten;

  openAction |= OPEN_ACTION_CREATE_IF_NEW;
  openAction |= OPEN_ACTION_REPLACE_IF_EXISTS;
  openMode |= OPEN_ACCESS_WRITEONLY;
  openMode |= OPEN_SHARE_DENYWRITE;
  if(!DosOpen("temp.txt",
               &fq,
               &action,
               newsize,
               fileAttr,
               openAction,
               openMode,
               NULL)) {
    for (x = 0; x < 2000; x++) {
      if(DosWrite(fq,buf,sizeof(buf),&actualWritten))
        break;
    }
    DosClose(fq);
  }
  return 0;
}

--- XHEd-OS/2 1.22