Re: [ON TOPIC] HELP: Getting lousy memory throughput from Abit KD7

From: Valdis.Kletnieks@vt.edu
To: root@chaos.analogic.com
Cc: Timothy Miller <miller@techsource.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [ON TOPIC] HELP: Getting lousy memory throughput from Abit KD7
Date: Tue, 22 Jul 2003 15:53:50 -0400	[thread overview]
Message-ID: <200307221953.h6MJroXb001837@turing-police.cc.vt.edu> (raw)
In-Reply-To: Your message of "Tue, 22 Jul 2003 15:34:51 EDT." <Pine.LNX.4.53.0307221520290.5609@chaos>

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On Tue, 22 Jul 2003 15:34:51 EDT, "Richard B. Johnson" said:

> If I needed to really find the memory access time, I would write
> a program to test it.

> (4) Warm the cache first by reading everything in the buffer you
>     are going to test.

At which point you're measuring the cache speed not the memory speed.

> You will probably be amazed at how well your system performs. This
> dual CPU 400 MHz thing, with 100 MHz memory does 1,900++ MiB/sec.

Which probably explains this result.  Do a quick sanity check - this number
seems to indicate 20 bytes per memory clock, EVERY clock - either there's
some VERY creative use of prefetching to make sure that you never hit a
cache line miss, or you're measuring the cache.. ;)

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