On Sat, Jul 15, 2006 at 07:13:10PM +0200, A. Liemen wrote:
> during some xfs tuning tests I discovered the following phenomenon.
> Maybe someone can explain it to me:
> Bonnie++ Reading with getc()... hits exactly an almost constant
> 65536 kbyte/s with only ~15% IO usage.
> iostat and bonnie output can be found under:
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
storage4 40000M 64890 99 229195 39 105826 24 63895 98 350285 38 361.1
It's cpu bound, not I/O bound. It can't go any faster because it's a
single threaded test....
> CPU usage is 100% (on one of the cpus) but i don't think that's the
> limiting factor since it hits that 16bit value absolut constantly.
What you are seeing is XFS issuing regular sized I/Os at a constant
If you really think this is a 16bit ceiling, see what the block I/O tests
report in iostat - you're getting ~230MB/s for write and 350MB/s for read, so
if iostat is has a bug then you'll see it there.
> Also of interest would be why the random seeks are so bad.
Try creating more than 16 files for youre create/read/delete so
that the runtime is somewhat greater than the timer resolution....
SGI Australian Software Group