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Date: Fri, 27 Feb 2015 19:56:10 +0400
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To: Jordi Boggiano <j.boggiano@seld.be>
Cc: PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Re: Zend JIT Open Sourced
From: dmitry@zend.com (Dmitry Stogov)

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On Fri, Feb 27, 2015 at 6:40 PM, Jordi Boggiano <j.boggiano@seld.be> wrote:

> On 27/02/2015 15:19, Andi Gutmans wrote:
>
>>
>>  On Feb 27, 2015, at 7:12 AM, Anthony Ferrara <ircmaxell@gmail.com>
>>> wrote:
>>>
>>> Dmitry and Zend,
>>>
>>> Thank you for sharing your code. I look forward to playing with it.
>>>
>>> Perhaps after 7 stabilizes (and ships) you could write up your
>>> thoughts around it? Why decisions were made and the findings that you
>>> have?
>>>
>>
>> Yes I think we can definitely do that. It is an interesting experiment
>> and clarified also that JIT was less interesting in the short term as we
>> can all observe by the fabulous results of the current PHP 7 runtime. But
>> absolutely worth discussing post 7 as there surely are interesting
>> opportunities.
>>
>
> Do you have a one line summary of why it's useless for real world
> applications? Is it just because they don't do enough number crunching
> compared to I/O or is it a matter of the JIT not kicking in fast enough to
> improve things in a single request cycle?
>

It's not a single request cycle. JIT integrated into opcache, it compiles
php script(s) of first access and stores code in shared memory.
On following requests precompiled code is executed directly from shared
memory.

- The first request may be extremely slow (few minutes)

- The speed improvement on the following request may be insignificant or
even negative. It very depends on application, but from my experience only
small apps got significant improvements. This may be explained by huge
increase in ICACHE and ITLB misses, but I'm not 100% sure.


> I am biased but if it improves the bench code so much it still sounds like
> a potentially good things for specific code like the composer dependency
> solver :)
>

Yeah. Probably, if we position this work as a JIT for hotspots only, or
even enable it for some functions manually we may get better results.

Thanks. Dmitry,


>
> Cheers
>
>
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