Messages in this thread | | | Subject | Re: 2.4, 2.6, i686/athlon and LDT's | From | Arjan van de Ven <> | Date | Mon, 27 Dec 2004 22:29:17 +0100 |
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On Mon, 2004-12-27 at 15:55 -0500, Brian Gerst wrote: > Arjan van de Ven wrote: > > On Mon, 2004-12-27 at 11:46 -0800, Tymm Twillman wrote: > > > >>Hi all, > > > > > >>It appears that use of the LDT is to speed up context switching between > >>threads, although I haven't even found especially good references WRT > >>that. I have looked through the info in the IA Developers publications > >>and have whacked my head against Google quite a bit. However, every bit > >>of clarity I've found there has been offset by new confuzled bits. > > > > > > LDT's are *slow*. That's why glibc will try to avoid using them > > nowadays, and with 2.6 it won't; as for 2.4.. it depends if you use a > > vendor 2.4 it might be able to avoid using LDT's as well. > > Using the LDT isn't inherently slower, since the cpu caches the segment > descriptor regardless of if it came from the GDT or LDT.
it does however increase context switch costs significantly since the LDT needs to be reloaded and reverified...
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