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Date: Tue, 26 Dec 2000 11:58:34 -0200 (BRDT)
From: Rik van Riel <riel@conectiva.com.br>
To: Felix von Leitner <leitner@convergence.de>
cc: linux-kernel@vger.kernel.org
Subject: Re: Abysmal RAID 0 performance on 2.4.0-test10 for IDE?
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On Tue, 26 Dec 2000, Felix von Leitner wrote:
> Thus spake Felix von Leitner (leitner@convergence.de):
> > Here is the result of my test program on the strip set:
> >   # rb < /dev/md/0
> >   30.3 meg/sec
> >   #
> 
> One more detail: top says the CPU is 50% system when reading from either
> one of the disk or raid devices.  That seems awfully high considering
> that the Promise controller claims to do UDMA.
> 
> Any comments?

Your program reads in data at 30MB/second, on a memory bus
that most likely supports something like 60 to 100MB/second.

Part of this memory bandwidth is needed for the UDMA controller
to push the data to memory, probably between 30% and 50%.

Every time the UDMA controller has the memory bus for itself the
CPU will busy-wait on memory, which shows up as CPU busy time.

regards,

Rik
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