[ltp] Re: Memory bandwith result from Memtest 86+?

[Daniel Pittman]

--=-=-=
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

Jan Kundr=C3=A1t <jkt@gentoo.org> writes:
> jqian@physics.harvard.edu wrote:
>> memtest 86+. A line in the screen piqued my interest: it shows that my=20
>> memory bandwidth is "1454MB/s". I'm not a memory expert at all, but my=20
>> two identical memories are VS1GSDS533D2, PC2-4200 DDR2 ram at 553MHz,=20
>
> Check the frequency of RAM that memtes86+ reports. On my T60, it varies
> from boot to boot, probably due to power management. I suspect that
> memtest86+ does its benchmarking stuff just for a while and that whoever
> is in charge of PM during that time (BIOS?) doesn't react fast enough to
> increase the frequency.

I wouldn't trust memtest86+ as an effective benchmark, not least of
which because it really isn't designed to benchmark so much as stress
test.

>> What kind of application will make memory bandwidth its main
>> bottleneck?
>
> Those that need simultaneous access to huge amounts of data. I guess
> that number-crunching applications and other stuff doing heavy
> computation (CAD?, compilers?). Given the horse power of any recent
> x86 computer, I'd say you won't notice much slowdown :).

Sadly, no.  The biggest thing that will notice the main memory speed is
every little thing you do, especially interactive GUI tools, because
they need more data than fits into your cache.

Unless you run very CPU intensive processes (like a compiler) that need
a limited quantity of data (for small chunks of code) then you usually
fall out of cache into slower memory.

Your web browser, for example, will comfortable use more than the 8MB of
L3 cache you get in the best equipped CPU these days -- let alone what
shows up in the Thinkpad mobile CPU lines.=20

Faster memory is the second /best/ investment you can make to improve
overall performance of your laptop, following only faster disks.

Regards,
        Daniel
=2D-=20
Daniel Pittman <daniel@cybersource.com.au>           Phone: 03 9621 2377
Level 4, 10 Queen St, Melbourne             Web: http://www.cyber.com.au
Cybersource: Australia's Leading Linux and Open Source Solutions Company

--=-=-=
Content-Type: application/pgp-signature

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)

iD8DBQFHTrp3ttyxN73O8xERAkOhAJ96lW5OB2DrYqV8w7jFTc5qRh1KbQCcC/MO
JAZFo6YmUr9UGqRHILgkwVs=
=gt10
-----END PGP SIGNATURE-----
--=-=-=--