kernel designations question

James Wilkinson fedora at westexe.demon.co.uk
Sun Dec 4 21:34:07 UTC 2005


Tony Foster wrote:
> I am fairly new to Linux but I was fairly good with unix 10 years ago.
> I am assuming that the kernel with the SMP tag is for HW with multiple
> processors?
>
> If so then the question is will that SMP kernel be well behaved on a
> Single processor hardware?  I would expect it to be well behaved but
> PC hardware sometimes surprises me.

Kam Leo wrote:
> Yes, if you are using a hyperthread enabled P4.

I think that's slightly misleading.

A hyperthreading Pentium 4 or Xeon "looks" to software like two
processors, and usually performs slightly better when used as two
processors rather than when used as one (ie when hyperthreading isn't
used). So a hyperthreading processor *needs* an SMP kernel to get that
extra performance.

On the other hand, Windows XP will expect to use both "virtual"
processors in SMP mode, so hardware aimed for such systems should at
least be able to run Windows in SMP mode. And, of course, any hardware
aimed at servers would be expected to work in SMP mode.

The various ranges of dual core processors also need SMP kernels, and
the performance increase you can get is a lot more.

As other posters have said, Tony is right: SMP kernels *should* work on
single processor systems, but PC hardware is not always well behaved.

James.

-- 
E-mail address: james |    "Just for once, I wish we would encounter an
@westexe.demon.co.uk  | alien menace that wasn't immune to bullets..."
                      |     -- The Brigadier, 'Doctor Who'




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