Date: Thu, 19 Jun 2003 16:22:33 -0700 (PDT) From: Julian Elischer <julian@elischer.org> To: Daniel Eischen <eischen@vigrid.com> Cc: Marcel Moolenaar <marcel@xcllnt.net> Subject: Re: Implementing TLS: step 1 Message-ID: <Pine.BSF.4.21.0306191621410.41210-100000@InterJet.elischer.org> In-Reply-To: <Pine.GSO.4.10.10306191913380.9608-100000@pcnet5.pcnet.com>
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On Thu, 19 Jun 2003, Daniel Eischen wrote: > On Thu, 19 Jun 2003, Julian Elischer wrote: > > > > BTW Marcel, I think that we can get from where we are now with kse to > > what we need by just a little massaging of what points to what. > > it is possible that the register %gs could be pointed to the thread > > structure directly and we could derive the KSE from that. it will just > > make the context switches a fraction more expensive if we need to > > change the segment register.. > > > > The big cost is that a processin x86 can only have a limited number of > > segments set up in teh Local descriptor table (LDT). > > I forget the actual number but i vaguely remember that it is 16383 or > > 8191 or something.. A process could theoretically want to have > > more than that numbe rof threads.. By pointing to the KSE we limit > > ourselves to having to set up onl a small number of LDT entries > > which is a big saving. > > Yes, and we can have thousands and thousands of threads. > > > On ia64 we don;t need to use descriptors so there is not that limit so > > in effect we could point directly to the thread descriptor and let THAT > > point to teh VCPU mailbox in question. it's just an extra write or two > > at context switch time. I think we'll be just fine. > > It is not just that. It is the cost of an ldt allocation for > each thread. In libkse, we only need as many LDTs as there > are KSEs. Allocating an ldt per-thread increases thread > startup and teardown. that's sort-of-what I was saying.. I think we are ok anyhow.. the spec for i386 is general enough so that we can use it as it is without problem. > > -- > Dan Eischen > >
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