From: Arjan van de Ven <arjan@infradead.org>
To: Brian Gerst <bgerst@didntduck.org>
Cc: Tymm Twillman <ttwillman@penguincomputing.com>,
linux-kernel@vger.kernel.org
Subject: Re: 2.4, 2.6, i686/athlon and LDT's
Date: Mon, 27 Dec 2004 22:29:17 +0100 [thread overview]
Message-ID: <1104182957.4187.18.camel@laptopd505.fenrus.org> (raw)
In-Reply-To: <41D076D9.30404@didntduck.org>
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...
next prev parent reply other threads:[~2004-12-27 21:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-12-27 19:46 Tymm Twillman
2004-12-27 20:22 ` Arjan van de Ven
2004-12-27 20:55 ` Brian Gerst
2004-12-27 21:29 ` Arjan van de Ven [this message]
2004-12-27 23:44 ` Ulrich Drepper
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