Re: [Xen-ia64-devel] RE: in_tpa is not SMP-safe

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Jeudi 09 Mars 2006 19:14, Magenheimer, Dan (HP Labs Fort Collins) a écrit :
> > > I was hoping Kevin would respond to this as my memory
> > > on it is dim.  There was a rare but significant problem
> > > that this code was fixing and we went through several
> > > attempts to fix it.  I don't think we ever understood
> > > exactly why this code was necessary because we (both
> > > Kevin and I) thought a different code sequence should
> > > work, but it didn't.
> > >
> > > So, yes, make the change to make it SMP-safe (I prefer
> > > the parameter), but be careful about changing the
> > > "in_tpa" semantics without running a very thorough
> > > test suite.
> >
> > Ok.
> >
> > Also, vcpu_translate look in itr_regions even for
> > data_access.  There is a
> > comment about that:
> > // FIXME?: check itr's for data accesses too, else bad things happen?
> > I suppose this is required to read instructions from Xen.
> > Are there any other
> > uses ?  Is it too dangerous to try to fix that ?
>
> It is certainly dangerous to change any of this code.  I spent
> several days playing with it (to improve performance) last
> October and was often surprised when a change broke everything.
> I definitely tried to fix the specific code you are referring
> to but never got it to work, ran out of time, and gave up.
>
> If you do try any changes, make sure it is tested VERY thoroughly
> as sometimes the problems I saw only showed up infrequently
> (e.g. compiling Linux failed 10 in 20 times instead of just 1
> in 20 times).
I don't want to make change now.
I'd just like to understand this function and the kludges.  I only regret the 
lacks of comments (no offense here).

Tristan.


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