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Date: Mon, 17 Jan 2022 11:13:45 -0600
To: "php internals" <internals@lists.php.net>
Content-Type: text/plain
Subject: Re: [PHP-DEV] Reason for ZEND_JIT_COUNTER_INIT set to 32531?
From: larry@garfieldtech.com ("Larry Garfield")

On Mon, Jan 17, 2022, at 6:12 AM, Dmitry Stogov wrote:
> Oh, probably this is just the biggest prime number that fits into a signed
> 16-bit number :)

Seems like the sort of thing that should be documented inline.  (Also, why it needs to be a prime number.)

--Larry Garfield

> On Mon, Jan 17, 2022 at 10:49 AM Su, Tao <tao.su@intel.com> wrote:
>
>> Thanks Dmitry for the information.
>>
>> With a few debug sessions, I found that 32531 is working well
>> for any thresholds, and is also a big prime number :-).
>>
>>
>> -----Original Message-----
>> From: Dmitry Stogov <dmitrystogov@gmail.com>
>> Sent: Monday, January 17, 2022 1:37 PM
>> To: Su, Tao <tao.su@intel.com>
>> Cc: PHP internals <internals@lists.php.net>
>> Subject: Re: [PHP-DEV] Reason for ZEND_JIT_COUNTER_INIT set to 32531?
>>
>> This it's my choice.
>> This number is common for all JIT counters (hot_loop, hot_func,
>> hot_return).
>> It's value was selected to provide the best precision when different
>> counters have different thresholds.
>> Unfortunately, I can't remember the exact equations or logic I used at
>> that time.
>>
>> Thanks. Dmitry.
>>
>> On Thu, Jan 13, 2022 at 1:01 PM Su, Tao <tao.su@intel.com> wrote:
>>
>> > Hi Internal,
>> > I am not sure this is a correct mail list for asking source code
>> > related question.
>> > If not, I am sorry. Appreciate you guys' help.
>> >
>> > I am reading PHP8 JIT related source code and found that zend_jit.h
>> > has a magic definition ZEND_JIT_COUNTER_INIT as 32531 which I do not
>> > quite understand how this number was chosen and why?
>> > Anybody can provide some historic information?
>> > #define ZEND_JIT_COUNTER_INIT         32531
>> >
>> > A code example using this definition (looks like the 2nd parameter
>> > computes into a fixed number if hot_func is set by php.ini)
>> > ZEND_OPCODE_TAIL_CALL_EX(zend_jit_trace_counter_helper,
>> >                 ((ZEND_JIT_COUNTER_INIT + JIT_G(hot_func) - 1) /
>> > JIT_G(hot_func)));
>> >
>> >
>> > =======================================
>> > Tony Su (Su, Tao)
>> > make a 'lazy' programmer diligently with efficiency
>> >
>> >
>>