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)
Note that linux seems to play tricks (zero copy?) when doing dd if=/dev/zero
of=/dev/null, because you can reach speeds which are way above the
theoretical maximum. (30GB/sec on a P4 1,6Ghz ??? no way)
In the context of databases, I think the speeds are limited by the processing
done on the data, as long as the read speed stays above a certain limit.
Yeah - typically it is creating tuples out of the blocks/pages just
read, so for a big memory scan CPU appears to be the limiting factor!
It would be more interesting to see how random access to a (cached) file
performs in Linux vs FreeBSD, which seems a more logical pattern for a
database.
Agreed, and good point, I'll knock up a simple program to do random
and/or sequential access of a file and see what we get!
Cheers
Mark
_______________________________________________
freebsd-stable@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-stable
To unsubscribe, send any mail to "[EMAIL PROTECTED]"
