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Date: Mon, 20 Dec 2004 22:00:41 +0200
From: "Eli Zaretskii" <eliz AT gnu DOT org>
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In-reply-to: <41c5fcca.sandmann@clio.rice.edu> (message from Charles Sandmann
	on Sun, 19 Dec 2004 16:12:26 CST)
Subject: Re: DMA and PIO (was Re: Problems with timer interrupt chaining and SmartDrv)
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> From: Charles Sandmann <sandmann AT clio DOT rice DOT edu>
> Date: Sun, 19 Dec 2004 16:12:26 CST
> 
> Try this test.  Open task manager so you can monitor CPU usage.  Using the 
> default DMA, read a 500MB file from disk.  Using a modern disk this should 
> take less than 10 seconds and use no more than 2-3 percent of the CPU.

What program does one use to read a file, but otherwise do nothing?

I used a native Windows port of GNU wc, which does some simple and
usually insignificant processing with the file it reads, and it took
it 20 seconds to read a 750MB file, using 20% of CPU.  This is on a
2.8GHz XP box, FWIW.  (And yes, "My Computer" does show that DMA is
being used, so sorry for spreading disinformation.)  I didn't try to
reboot with PIO.

By contrast, on a 450MHz Pentium II MMX running Windows 98, where the
(bus-mastering) disk controller uses something called "dual fifo"
instead of DMA, reading a 515MB file via wc took 180 seconds (and the
CPU usage went through the roof).  That's a factor of 13 for a sixfold
increase in CPU speed (but I think that we should compare PCI bus
speed, not CPU speed) -- shouldn't a decent DMA speed things up much
more?