[GRLUG] Cores / Performance [Was: virtual box/cpu speed]

[Adam Tauno Williams]

On Thu, 2011-03-24 at 03:21 +0000, Michael Mol wrote:
> If you use soft RAID on Linux, and have the appropriate kernel option
> enabled, checksum calculations for RAID modes 4, 5, and 6 will be
> split across your cores.

+1 And ever since MMX was introduced to CPUs RAID calculations are
accelerated and *fast*.

> Desktop apps are catching up, too. If you use Firefox, Flash is kept
> as a separate process, a scenario which benifits from more cores (see
> my note on latency near the beginning). If you use Chrome or Chromium,
> each _tab_ is a separate process, which leverages multicore for
> app-wide performance improvements.

IE does this as well, and it is on the roadmap for FF.   

Multiprocessing is in general a nice approach now that we have solidly
debugged IPC mechanisms.

> These days, hanging at two cores when looking at making a purchase
> doesn't make sense.

+1

> Right now, I believe the price/performance sweet spot is at three
> cores. It will probably be at four by the end of summer.

Probably about right;  although the i7 has four cores, and 2/4/6 seems
the standard increment.  On my quad-core i7 laptop I see that I can busy
out two cores at which point I believe other constraints start to kick
in.  The machine remains usable/responsive [I think thanks to the other
cores and a modern OS kernel] but throughput for expensive processes
clearly starts to drop off.  I'd assume on a server, with better I/O
capacity, the threshold would be some what higher.  However you are
still going to start to congest the cache and main-memory channels -
which generally still can't really handle feeding 4 - 6 cores at full
speed [Maybe if you get an IBM Power 7 box? mmmmmm...]

And as a sys-admin I feel compelled to repeat the mantra "I/O, I/O, it
is off to work we go...".   Pitch all the CPU horsepower, cloud magick,
whatever... at a problem you want - the hard part is I/O and getting
data to/from mass storage.  I/O & storage is, in every scenario, the
expensive part.  

Aside: the Toshiba Qosmio series laptops can house two hard drives, now
*that* is tempting in conjunction with an i7.  Put workflow data on an
SSD and still have a big spinner for the OS, VMs, and all the other
cruft that just lays around. 


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