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SubjectInvalid perf_branch_entry.to entries question
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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




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