Re: tuning for large files in xfs

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



>
> What's your testing methodology?
>

here is my code... pretty simple, opens the file and reads around to a random block, 32k worth (note, doing a 2k read doesn't make much of a difference, only marginal, from 6.7ms per seek down to 6.1).

int main (int argc, char* argv[]) {
  char buffer[256*1024];
  int fd = open(argv[1],O_RDONLY);
  struct stat s;
  fstat(fd,&s);
  s.st_size=s.st_size-(s.st_size%256*1024);
  initTimers();
  srandom(startSec);
  long long currentPos;
  int currentSize=32*1024;
  int startTime=getTimeMS();
  for (int currentRead = 0;currentRead<10000;currentRead++) {
    currentPos=random();
    currentPos=currentPos*currentSize;
    currentPos=currentPos%s.st_size;
    if (pread(fd,buffer,currentSize,currentPos) != currentSize)
    std::cout<<"couldn't read in"<<std::endl;
  }
std::cout << "blocksize of "<<currentSize<<"took"<<getTimeMS()-startTime<<" ms"<<std::endl;
}

> You can try to measure the amount of seeks going to the disk by using
> iostat, and see if that matches your test program.
>

I used iostat and found exactly what I was expecting: 10,000 rounds x 16 (number of 2k blocks in a 32k read) x 4 (number of 512 blocks per 2k block) = 640,000 reads, which is what iostat told me. so now my question remains, if each seek is supposed to average 3.5ms, how come I am seeing an average of 6-7ms?

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux