Re: AMD Shanghai versus Intel Nehalem

On Wed, 13 May 2009, Scott Carey wrote:

> Can you do a quick and dirty memory bandwidth test? (assuming linux)
>
> /sbin/hdparm -T /dev/sd<device>
>
> ...its not a very accurate measurement, but its quick and highlights
> relative hardware differences very easily.

I've found "hdparm -T" to be useful for comparing the relative memory
bandwidth of a given system as I change its RAM configuration around, but
that's about it.  I've seen that result change by a factor of 2X just by
changing kernel version on the same hardware.  The data volume transferred
doesn't seem to be nearly enough to extract the true RAM speed from
(guessing the cause here) things like whether the test/kernel code fits
into the CPU cache.

I'm using this nowadays:

sysbench --test=memory --memory-oper=write --memory-block-size=1024MB
--memory-total-size=1024MB run

The sysbench read test looks similarly borked by caching effects when I've
tried it, but if you write that much it seems to give useful results.

P.S. Too many Scotts who write similarly on this thread.  If either if you
are at PGCon next week, please flag me down if you see me so I can finally
sort you two out.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD