On Mon, 16 Aug 2021 09:29:16 PDT (-0700), Kito Cheng wrote:
> Could you submit v3 patch which is v1 with overlap_op_by_pieces field,
> testcase from v2 and add a few more comments to describe the field?
>
> And add an -mtune=ultra-size to make it able to test without change
> other behavior?
>
> Hi Palmer:
>
> Are you OK with that?
I'm still not convinced on the performance: like Andrew and I pointed
out, this is a difficult case for pipelines of this flavor to handle.
Nobody here knows anything about this pipeline deeply enough to say
anything difinitive, though, so this is really just a guess.
So with an extra field to indicate should resolve that?
I believe people should only set overlap_op_by_pieces
to true only if they are sure it has benefits.
My only issue there is that we'd have no way to turn it on, but see
below...
As I'm not convinced this is an obvious performance win I'm not going to
merge it without a benchmark. If you're convinced and want to merge it
that's fine, I don't really care about the performance fo the C906 and
if someone complains we can always just revert it later.
I suppose Christoph has tried with their internal processor, and it's
benefit on performance,
but it can't be open-source yet, so v2 patch set using C906 to demo
and test that since that is
the only processor with slow_unaligned_access=False.
Well, that's a very different discussion. The C906 tuning model should
be for the C906, not a proxy for some internal-only processor. If the
goal here is to allow this pass to be flipped on by an out-of-tree
pipeline model then we can talk about it.
I agree on the C906 part, we never know it's benefit or not, so I propose
adding one -mtune=ultra-size to make this test-able rather than changing C906.
That's essentially the same conclusion we came to last time this came
up, except that we were calling it "-Oz" (because LLVM does). I guess
we never got around having the broader GCC discussion about "-Oz". IIRC
we had some other "-Oz" candidates we never got around to dealing with,
but that was a while ago so I'm not sure if any of that panned out.
