On Sun, 2006-05-28 at 20:04 +0200, Carlos E. R. wrote:
Why is that? I'm curious. Can't it use dma, even if it uses smaller writes? Just guessing.
Because all writes are Programmed I/O (PIO) through the CPU. XOR might be simple, but attempting to deal with the traditional LOAD/EXEC/STOR through the CPU -- even using streamed XOR operations -- at hundreds of MBps is still damn slow through. CPUs are not I/O processors (IOP). And such IOP operations take away from other operations. So unless your system is a dedicated storage device, and not servicing anything else (which is fine), you're taking away from your other operations. And, again, it's virtually _impossible_ to measure these metrics in the current Linux kernel. All you can find out is I/O wait and servicing for processes, not the I/O latency and throughput itself. -- Bryan J. Smith Professional, technical annoyance mailto:b.j.smith@ieee.org http://thebs413.blogspot.com ----------------------------------------------------------- Americans don't get upset because citizens in some foreign nations can burn the American flag -- Americans get upset because citizens in those same nations can't burn their own