Re: Hardware limits on numbers of threads?

From: Denis Vlasenko (
Date: Wed Sep 18 2002 - 06:37:58 EST

On 18 September 2002 04:43, Dan Kegel wrote:
> 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 ;-).

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

This archive was generated by hypermail 2b29 : Mon Sep 23 2002 - 22:00:22 EST