Hyperthreading hurts 5.3?

Giorgos Keramidas keramida at ceid.upatras.gr
Wed Jan 12 09:51:59 PST 2005

On 2005-01-12 18:41, Anthony Atkielski <atkielski.anthony at wanadoo.fr> wrote:
> Giorgos Keramidas writes:
> GK> You need to enable SMP too, to allow the FreeBSD kernel to use the
> GK> second (hyper-threaded) CPU.
> I found it, in a file called SMP.  Why is the SMP option tucked away in
> a separate file? [...]

The 'separate file' is NOTES.  This file is actually the complete
reference of options that the kernel supports, so it's not like the SMP
option is hidden or something.

> I imagine this will give me a bit more horsepower for the buck,
> although--with only 0.2% of the machine busy under normal load even with
> a single processor--I guess I wasn't exactly processor-bound to begin
> with (I'd run out of I/O capacity long before running out of processor).
> But why not profit from what's there, eh?

Because it's not always a 'profit'.

The locking and synchronization overhead is not always negligible.
Please, read the rest of the thread too :-)

- Giorgos

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