Re: [PATCH] perf, x86: Add workaround for MEM_*_RETIRED errata BV98

[Peter Zijlstra <peterz@infradead.org>]

On Mon, May 06, 2013 at 07:41:54PM +0200, Stephane Eranian wrote:

> Problem is, those events are really important. We need to be able to
> measure them.

At what cost? If the code we need to make it work is horrendous we need to
maintain that too -- possibly quite a lot longer than Intel thinks IVB is
relevant.

Anyway; since these events are immediately dangerous (they corrupt state)
blocking them is the right thing; we can always merge a patch that undoes that
once we've figured out a sane way.

Currently I'm still waiting for someone to explain (in complete detail) how the
corruption manifests. Until that is clear I can't even begin formulating what
might be needed to make it work again.

One mode that makes sense to me is where CNTx on SMTi corrupts CNTx on SMTj for
i != j. However there's also been said that the only case that doesn't corrupt
is for SMTj to have all counters disabled -- which contradicts the previous
case.

The former case we could maybe make work; the latter I can't see how we could
possible make work at all.