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Date: Thu, 25 Sep 2003 20:20:59 -0400 (EDT)
From: Daniel Eischen <eischen@vigrid.com>
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To: David Xu <davidxu@FreeBSD.org>
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Subject: Re: THR and KSE platform support (again)
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On Fri, 26 Sep 2003, David Xu wrote:

> On Friday 26 September 2003 06:57, Daniel Eischen wrote:
> > > I have some ideas may not related to this topics:
> > > On alpha, we need Memory Barrier for kse_crtical_enter.
> > > Because we always have following access pattern:
> > > kse_critical_enter();
> > > KSE_SCHED_LOCK(curthread->kse, curthread->kse->k_kseg);
> > > if there is no Memory barrier in kse_critical_enter, then
> > > read ahead of curthread->kse by CPU is wrong.
> > > I have a small patch for kcd_critical_enter for alpha.
> >
> > I thought atomic_{load,store}_{acq,rel} would give us
> > appropriate memory barriers.  Or are we not always using
> > these functions where we should be?
> >
> kcb_critical_enter on alpha is not using atomic instructions,
> out of order read/write makes kcb_critical_enter not work
> on SMP.

Yes, I see what you mean.  If it is isolated to MD
functions like kcb_critical_enter() I would either
use the atomic_ functions, or add the memory barrier
directly to those functions.  Hopefully, we can keep
MI parts free of memory barriers.

-- 
Dan Eischen