Mailinglist Archive: opensuse (5130 mails)

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Re: [SLE] Re: DMA, ATA standards, etc... -- WAS: Advantages of Dual Core
  • From: "Bryan J. Smith" <b.j.smith@xxxxxxxx>
  • Date: Mon, 29 May 2006 11:22:38 -0400
  • Message-id: <1148916158.2724.246.camel@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
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
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

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