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Re: SMP on Debian server with Hyperthreading


On Fri, 2003-09-05 at 17:06, Jason Lim wrote:
> Hi all,
> Just wondering... I've got a 2.4Ghz Hyperthreading (100% it is the
> hyperthreading model), and the BIOS sees it.

I have a 3.06 GHz P4 on an I845G chipset and in the BIOS I had to switch
the HT option from disabled to enabled. So is it actually on in your

> I then compiled the kernel... the usual, except added the SMP support
> setting "Symmetric multi-processing support". Nothing else was changed.
> Compiled it, liloed it... it's running it:
> # uname -a
> Linux megalith 2.4.22 #8 SMP Thu Aug 28 14:44:13 HKT 2003 i686 unknown
> However,

That's correct.

> # mpstat -P
> Not an SMP machine...
> And in top i don't see the multiple CPU usage....

This does work on my setup. I'm running 2.4.22 now, but it worked with
2.4.20 aswell.

> this is all strange. For Linux, aren't Hyperthreading CPUs suppose to act
> like completely separate independent CPUs (this was suppose to change in
> 2.6... but for 2.4, they can't tell the difference, right?).
> Hope you can advise... as hyperthreading is there but not being used,
> which is a waste and could add performance.

My machine is a workstation, so I don't know what would happen with
typical server software (ie apache, database) but for instance compiling
a kernel with 3 simultaneous threads is about 20% faster than using only
1 thread.

> Thanks in advance!

Hope this helps!

> Jas


Guus Houtzager                           Email: guus@houtzager.net
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          "A)bort, R)etry, I)nfluence with large hammer."

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