Re: [PATCH 11/11] [v4] drm/i915/bdw: Ensure a context is loaded before RC6

Daniel Vetter
2014-03-20T13:42:39Z

On Wed, Mar 19, 2014 at 05:41:37PM -0700, Ben Widawsky wrote:
> I can't say it's completely unexpected that this would be your response,
> but I do feel like you've ignored my argument that this is better than
> the current situation. Not merging this patch only keeps things bad.
>
> So I'd like you to re-consider merging this patch instead of waiting for
> the perfect solution. This patch requires a lot less review than the
> real fix. It has been tested by several people (I can ask them to put
> their reviewed by on it). It enables rc6 for people today, and this
> includes pc7, and deeper package and C states. It's very easy to revert
> if/when we get a real fix. Real users benefit from this patch. Real
> users are not hurt by this patch because if userspace is submitting bad
> state setup, they'll have the same or worse experience than failing RC6.
>
> As an aside, this needs to come before I enable rc6 anyway. So the order
> way bad.

I fully agree with your assessment on technical reasons. The problem is
that I've just been forced through an exercise of "merge this now because
it works, people have tested it and we really, really, really need it to
move forward" and it didn't go down well.

Which means for the foreseeable future I'll reject patches when it looks
like a few too many rolls of ducttape have been involved in their
construction. I'd prefer if we could move more towards a merge early or at
least integration-test early model, but currently that's not a viable
model for me.

Note that this is not an iron rule at all, e.g. with psr I've just told
Rodrigo that I want the current state of affairs finalized for merging
instead of trying to hunt for the perfect patches. The reason for that was
that I think the remaining issues in psr support are well-understood and
we have solid test-coverage to make sure we don't fumble things. Also one
issue with the current psr patches is that they're way too conservative in
a few cases (i.e. wasting power), but for something tricky leaning towards
correctness is actually a feature. And bad power numbers tend to grab our
project managements attention. Overall the risks are a fairly clear
quantity.

In this area of rc6 and contexts though we have track record of not really
understanding issues. Which means that the risks here are unknown and
might be fairly big.

Yours, Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch