From mboxrd@z Thu Jan  1 00:00:00 1970
From: lorenzo.pieralisi@arm.com (Lorenzo Pieralisi)
Date: Wed, 4 Jun 2014 16:51:29 +0100
Subject: [PATCH] arm64: topology: add MPIDR-based detection
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To: linux-arm-kernel@lists.infradead.org
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On Wed, Jun 04, 2014 at 02:54:31PM +0100, Mark Brown wrote:
> On Wed, Jun 04, 2014 at 02:01:14PM +0100, Lorenzo Pieralisi wrote:
> > On Wed, Jun 04, 2014 at 12:57:51PM +0100, Mark Brown wrote:
> 
> > > > All I am saying is, let's wait and see, there is no compelling need to
> > > > use aff3 (and aff2 on non-SMT systems) on current systems for the
> 
> > > That's still a kernel patch or having to write DT to get things working
> > > which for the sake of avoiding a couple of shift and or statements just
> > > seems unhelpful.  If it was just going to give poor performance that'd
> > > be one thing but it's actively broken.
> 
> > What's broken ? Please provide me with an example and I will update the
> > patch.
> 
> If some system we encounter in the future is for example a SMT system
> which does use aff3 then until someone actively goes and fixes it by
> writing the DT/ACPI or updating the kernel if there's two threads
> 0,0,0,0 and 0,0,0,1 we'll tell the scheduler they're both 0,0,0 which
> we're not supposed to do.

Ok, so nothing to worry about for now (and as I mentioned that's a "bug"
in arm32 code too, less likely to be triggered, granted).

My question is: is it better to pack affinity levels and "guess" what aff3
(and aff2 on non-SMT) means or add an additional level of hierarchy in the
arm64 topology code (eg book_id - implemented only for s390 to the best
of my knowledge) ?

I personally prefer the latter approach but I think it boils down to
understanding what do we want to provide the scheduler with if we have
a hierarchy that extends beyond "cluster" level.

I will be glad to help you implement it when time comes (and this will also
fix the clusters of clusters DT issue we are facing - ie how to treat them).

Now, I do not think it is a major problem at the moment, merging the
patch I sent will give us more time to discuss how to define the
topology for clusters of clusters, because that's what we are talking
about.

Does it make sense ?

Thanks !
Lorenzo