[LLVMdev] RFC: Binary format for instrumentation based profiling data

["C. Bergström"]

On 04/19/14 02:47 AM, Chandler Carruth wrote:
>
> On Fri, Apr 18, 2014 at 12:22 PM, Evan Cheng <evan.cheng at apple.com 
> <mailto:evan.cheng at apple.com>> wrote:
>
>     I agree the top priority should always be "getting it right”. But
>     I can’t agree with this thinking completely. This has to be
>     balanced with pragmatism. If we completely disregard the practical
>     concerns of commercial use, it makes LLVM hostile towards an
>     important group of users.
>
>
> Clearly, I can't argue with that. =] We benefit from it as well. And I 
> don't think I'm arguing against a pragmatic approach in this case, 
> although I'm sorry if it comes off that way.
>
> Just so we're on the same page, the only real question in my mind is: 
> can we make breaking changes as we iterate on the design.
>
> What I would like to do is figure out the right design first, 
> incrementally, trying one format, and seeing how it does, but 
> potentially with backwards incompatible changes. Once we have the 
> experience and know what the right format is, *then* we should 
> consider pragmatic concerns such as how to structure support for 
> reading legacy formats, or formats outside of the control of the 
> project. I think if we start off with a format that we can't change 
> because of external reasons (whatever they may be), it will be much 
> harder to incrementally get to the right design. Does that seem 
> reasonable (and hopefully help explain the concrete suggestion I'm 
> making)?
Why can't we have our cake and eat it too?

Off the cuff and flame away
------------
What's wrong with a soft policy like - Feel free to do an incremental 
improvement which breaks a change and then if someone else wants to 
contribute a patch that allows the old format/behavior - that's up to 
them (patches welcome). Both changes would be accepted and allows the 
parallel paths - (putting the burden of maintenance for backward 
compatibility on those stakeholders). Wouldn't this solve the problem 
Right Now(tm)?

I don't mean this as an attack
It's very depressing to see passionate Apple vs Google people not be 
able to come to middle ground very quickly