Re: [Xen-ia64-devel] SMP designs and discuss

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Samedi 15 Octobre 2005 00:21, Magenheimer, Dan (HP Labs Fort Collins) a 
écrit :
[...]
> > * scheduler spin-lock.
> >   Currently, I use an hack to release the spin-lock acquired in
> >    __enter_schedule.  This is done in schedule_tail.
> >   The problem is during the first activation of a domain: the
> > spin-lock is
> >   acquired, but context_switch never returns, and on x86 the
> > spin-lock is
> >   released after context_switch.
>
> Not sure if there is a better solution than your hack but others
> may have suggestions.
Ok this issue may be closed.

> > * Idle regs.
> >   Currently, idle domains have no regs (the regs field is NULL).
> >   [I am not sure it is true for idle0].
> >   Is it a problem ?
> >   I had to modify the heartbeat so that it doesn't reference regs.
>
> Personally I don't think idle should exist, but it definitely
> shouldn't require state to be saved and restored.
Maybe true for idle0 but what do other processors execute when there is no 
domain ?

> > * Why xentime.c is so complicate ?
> >   What is the purpose of itc_at_irq, stime_irq ?
>
> Some of this is historical from my early attempts to leverage
> Linux code while merging in the necessary Xen code.  Time
> management needs to be rewritten but we have delayed working
> on it until higher priority tasks are done.
Ok

[...]
> > * VHPT
> >   How many VHPT per system ?
> >    1) Only one
> >    2) One per LP  (current design)
> >    3) One per VCPU (original Xen-VTI).
> >   I think (1) is not scalable...
>
> I thought the current design is (1).  Perhaps I didn't
> look closely enough at your SMP patch!
Well, the VHPT is allocated in mm_init, which is called once per cpu.

> There was some debate about this in April.  It started off-list
> but some of it is archived here:
> http://lists.xensource.com/archives/html/xen-ia64-devel/2005-04/msg00017
> .html
> We decided that different use models may require different
> VHPT models and that we would support both, at least so that
> we could measure them both.  This also hasn't been high priority
> as, until recently, we didn't have more than one LP or VCPU!
Ok, I will look the archives.

Tristan.


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