Re: [RFC] JIT

On Thursday, January 31, 2019 12:30:52 PM CST Chase Peeler wrote: > On Thu, Jan 31, 2019 at 12:04 PM Zeev Suraski <zeev@php.net> wrote: > > On Thu, Jan 31, 2019 at 6:47 PM Kalle Sommer Nielsen <kalle@php.net> > > > > wrote: > > > Without my usual Windows bias, I do believe it is a considerable fact > > > like Nikita pointed out as Windows is a first class citizen in terms > > > of operating systems we support. While PHP on Windows may not have the > > > speed that the Unix counterpart have, it is still a very important > > > development platform. Many developers develop on Windows and deploy on > > > a Unix based system, being unable to test such an important feature in > > > a development environment is also a large question mark. > > > > As long as we can agree that very few actually *deploy *on Windows, I > > think > > we're on solid grounds. > > As the JIT implementation is likely to have at least *some* significant > > differences compared to Linux, I'm not sure what testing it on Windows > > would give you. JIT is supposed to be entirely transparent, and the > > performance characteristics - as well as the bug patterns - are likely to > > be quite different on Linux vs. Windows, at least in many cases. > > Is it really that important to have? > > > > I'm honestly a bit perplexed by how many people here viewing Windows > > support as a must have, while at the same time I think we all agree PHP is > > very scarcely found on production Windows servers, and JIT is a > > predominantly production feature. > > > > I'm personally interested in taking a look at it (and I'm certain > > > > > Anatol does too), but simply dismissing is a no-go for me. > > > > It'd be interesting to evaluate the cost associated with supporting > > Windows. Bare in mind, we're proposing to vote on this as a production > > feature for PHP 8 - which realistically means almost two years from now > > *at > > the earliest*. I'm sure we'd have Windows support a lot sooner than that > > if we decide that it's a must have. I agree with Nikita that the key > > question is in fact, do we or do we not want to introduce JIT in - with > > the > > main question being the maintenance cost. Let's tackle this question > > first, otherwise - why send Dmitry (and maybe others) for doing more work > > (Windows support) if we are likely to flush it all down the toilet? > > > Maybe we're the only ones, but we run production PHP on Windows. I have no > issues with the idea of not initially having support for Windows. I can > probably even live with never having support for Windows - provided that we > don't find ourselves in a situation like Nikita mentioned where features > start getting developed in PHP instead of C and require JIT in order to > function. Question from a non-compiler-engineer: Could we end up in a situation where future language features (in 8.3 or something) are only performant on JIT- enabled platforms? I know there were some RFCs rejected in the past on the grounds that they involved too many runtime checks (and thus a performance hit); if it were possible for a JIT to optimize some of those away, it might make the cost acceptable. However, if a JIT only works on some systems that might widen the gap between have- and have-not platforms. Is that a concern, or am I making things up? Or, is it a concern but we're legit OK with that happening (which is also an entirely valid decision to make)? --Larry Garfield

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