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From: Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua>
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To: Dan Kegel <dank@kegel.com>, linux-kernel@vger.kernel.org
Subject: Re: Hardware limits on numbers of threads?
Date: Wed, 18 Sep 2002 09:37:58 -0200
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On 18 September 2002 04:43, Dan Kegel wrote:
> http://people.redhat.com/drepper/glibcthreads.html says:
> > Hardware restrictions put hard limits on the number of
> > threads the kernel can support for each process.
> > Specifically this applies to IA-32 (and AMD x86_64) where the thread
> > register is a segment register. The processor architecture
> > puts an upper limit on the number of segment register values
> > which can be used (8192 in this case).
>
> Is this true?  Where does the limit come from?

It is true that on x86 you have only 8192 different segment selectors
at a time. Nobody says you can't modify segment descriptors on demand.

If I'm not mistaken, Linux kernel does precisely this. It has per-CPU
allocated GDT entries, not per-task. So there is no limitation
unless you happen to have more than 1024 CPUs ;-).
--
vda
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