From mboxrd@z Thu Jan  1 00:00:00 1970
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From: Michael Neuling <mikey@neuling.org>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>, eranian@google.com
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Subject: Invalid perf_branch_entry.to entries question
Date: Tue, 07 May 2013 11:35:28 +1000
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Cc: Linux PPC dev <linuxppc-dev@ozlabs.org>, linux-kernel@vger.kernel.org,
 Anshuman Khandual <anshuman.khandual@in.ibm.com>
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Peter & Stephane,

We are plumbing the POWER8 Branch History Rolling Buffer (BHRB) into
struct perf_branch_entry.

Sometimes on POWER8 we may not be able to fill out the "to" address.  We
initially thought of just making this 0, but it's feasible that this
could be a valid address to branch to. 

The other logical value to indicate an invalid entry would be all 1s
which is not possible (on POWER at least).

Do you guys have a preference as to what we should use as an invalid
entry?  This would have some consequences for the userspace tool also.

The alternative would be to add a flag alongside mispred/predicted to
indicate the validity of the "to" address.

Mikey