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To: Larry Garfield <larry@garfieldtech.com>, "internals@lists.php.net"
	<internals@lists.php.net>
Thread-Topic: [PHP-DEV] [RFC] JIT
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Subject: Re: [PHP-DEV] [RFC] JIT
From: dmitry@zend.com (Dmitry Stogov)



On 2/1/19 3:29 AM, Larry Garfield wrote:
> 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 th=
at
>>> 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 wo=
rk
>>> (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.
>=20
> Question from a non-compiler-engineer: Could we end up in a situation whe=
re
> 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 t=
he
> grounds that they involved too many runtime checks (and thus a performanc=
e
> hit); if it were possible for a JIT to optimize some of those away, it mi=
ght
> make the cost acceptable.  However, if a JIT only works on some systems t=
hat
> might widen the gap between have- and have-not platforms.

I think, JIT only approach doesn't make a lot of sense for PHP, with one=20
of the most fast VM. And this is a trend. Even V8, starting from JIT=20
only, switched back to VM+JIT.

Thanks. Dmitry.

>=20
> 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)?
>=20
> --Larry Garfield
>=20