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

[linux-thinkpad@linux-thinkpad.org]

> 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 is a good benchmark for memory bandwidth under linux?
> 
> 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. 
Unless you get one of these monsters
http://en.wikipedia.org/wiki/Power6
32MiB of off die L3 Cache! I suppose firefox, fixing its memory leak, 
can be made fitting into those.
> 
> Faster memory is the second /best/ investment you can make to improve
> overall performance of your laptop, following only faster disks.
Unfortunately the upper limit of memory is set by the bus speed of a 
laptop, which is not easy to change for an laptop. For example, my 
laptop have a bus speed of 533MHz of its mainboard.

My disk is 7200RPM disk, which hdparm /dev/sda:
 Timing cached reads:   3436 MB in  2.00 seconds = 1719.02 MB/sec
 Timing buffered disk reads:  114 MB in  3.02 seconds =  37.72 MB/sec

Is that fast for a laptop? What's is that cached read? Is that a good 
benchmark for memory bandwidth?

Thanks for the education.
Jiang

> 
> Regards,
>         Daniel
> -- 
> 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