Cached file read performance with 6.2-PRERELEASE

Mark Kirkwood markir at
Thu Dec 21 03:52:53 PST 2006

Pieter de Goeje wrote:
> On Wednesday 20 December 2006 11:38, Mark Kirkwood wrote:
>> In fact if you note that the PIII HW *can* actually do 700MB/s, it
>> suggests that your HW is capable of considerably more than 900MB/s -
>> given that opteron's have excellent cpu to memory bandwidth, and the
>> speed of your memory!
> Indeed!
> Copying /dev/zero to /dev/null yields more than 5GB/sec on a simple 2Ghz 
> Athlon64. It imagine there are quite a few extra things done when copying a 
> file from cache, because I can only manage to get one fifth (~1GB/sec) of the 
> theoretical speed. (this is with a file that fills more than half of all 
> memory)

Fascinating, never thought of trying that! On my 2 (essentially) 
identical PIII systems, doing copy /dev/zero to /dev/null yields 4.1 
GB/s (Gentoo) and 2.0GB/s (FreeBSD)  - so yeah, clearly both do 
something special in that case... (growl... we - i.e FreeBSD - seem to 
be slower again...tho at that sort of rate, who cares!)



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