[r-t] Composition search?

[Alan Burlison]

On 25/11/2015 00:49, Alex Dicks wrote:

> How much speed up do you get with that level of SMT? I've never been
> convinced that Intel's hyperthreading makes that much difference, and have
> benchmarked C compilation on a 10-core/20-thread build server and found a
> plateau at "make -j10". I think it helps a bit if you miss cache often, or
> tend to use machine different instructions across threads/processes. But
> maybe SPARC has more SMT benefits.

It all depends. It's safe to say it's never linear and it's never easy 
to achieve. And cache misses are almost never good.

Generally what happens is you end up chasing the bottleneck from one 
place to another - for example in your compilation scenario it may well 
have been the disk that became a bottleneck, and not disk bandwidth 
which is what people normally look at, but IOs/second.

-- 
Alan Burlison
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