Re: cheap 8-core ARM board

[Reinoud Zandijk <reinoud%NetBSD.org@localhost>]

On Tue, Nov 22, 2016 at 02:52:03PM +0100, Christian Baer wrote:
> with OpenWRT. The new and fast ones are all ARM based. That isn't
> necessarily a bad thing but it noticeable. At the same time, the
> Chinese are making laptops with MIPS CPUs.

Really laptops with MIPS CPUs? Haven't seen one come by yet but maybe I wasn't
looking hard enough :)

My biggest problem with the ARM boards that are generally available is that
the CPU is OK but the memory bandwidth is just not up to spec. Esp. with the
PI1 and the PI2 (dont know about the PI3) the CPU can do a fair amount but
don't try to crunch data with it since its 16 bit databus cripples the entire
beast. Manipulating local data goes fast but as soon as you start processing
larger things it just slows down tremendously. I should compare my PI board
with both linux and NetBSD to see if it matters much; then we can exclude the
pmap stuff.

My current NAS, a LG Marvell board has the same performance problem. Next to
this the amount of `system time` it eats when streaming data to/from its SATA
over the gb network port is appalling. Sometimes in the 30-50% and you get a
few mb/sec max.

So yes, 8 cores might look fine but if they share a common 16 bit databus to
DRAM, then thanks but no thanks. There are board like the NVidea (Tegra?)
board that are exceptions on the rule but even then its max 32 bits wide
AFAIR.

Cheers,
Reinoud
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