Date: Mon, 29 Mar 2004 16:56:33 -0500 (EST) From: Daniel Eischen <eischen@vigrid.com> To: Doug Rabson <dfr@nlsystems.com> Cc: freebsd-threads@freebsd.org Subject: Re: Thread Local Storage Message-ID: <Pine.GSO.4.10.10403291651380.23090-100000@pcnet5.pcnet.com> In-Reply-To: <200403292250.31315.dfr@nlsystems.com>
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On Mon, 29 Mar 2004, Doug Rabson wrote:
> On Monday 29 March 2004 22:26, Daniel Eischen wrote:
> > On Mon, 29 Mar 2004, Doug Rabson wrote:
> > >
> > > Surely the GNU TLS ABI is preferable? It generates much smaller
> > > code and needs many fewer relocations.
> >
> > No, we don't want an LDT for every thread and don't want
> > to force a syscall for a thread switch.
>
> But the code it generates is at least twice the size for dynamic TLS. It
> seems that the GNU people have done a better job defining the TLS abi
> for i386.
About the only thing that uses TLS that I know is nvidia's
openGL. If you design an API correctly, there's no need
for TLS. I would hope that it's usage would be limited.
> You don't need a syscall at thread switch if you do something like:
>
> _thread_switch(...)
> {
> if (tcb doesn't have LDT entry) {
> if (!free LDT entries)
> steal LDT entry from non-running thread;
> allocate LDT entry and point it at TLS goop for tcb.
> }
> load_gs(tcb's LDT sel);
That's a system call on amd64.
> ...
> }
>
> I just have this feeling that the GNU ABI is going to get far better
> testing and support in the future since thats what linux uses.
--
Dan Eischen
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