# Reason for ZEND_JIT_COUNTER_INIT set to 32531? - Thread: https://externals.io/message/116878 - Original archive: https://news-web.php.net/php.internals/116878 - Started by tao.su@intel.com on 2022-01-13T10:01:40+00:00 - Messages: 6 - Reply by email to internals@lists.php.net - More for agents: search with https://externals.io/search.md?q={query} · JSON API at https://externals.io/api · documentation at https://externals.io/llms.txt --- ## #116878 — tao.su@intel.com — 2022-01-13T10:01:40+00:00 URL: https://externals.io/message/116878#116878 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 --- ## #116883 — Dmitry Stogov — 2022-01-17T05:36:52+00:00 URL: https://externals.io/message/116878#116883 · In reply to: #116878 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. > 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 --- ## #116884 — tao.su@intel.com — 2022-01-17T07:49:36+00:00 URL: https://externals.io/message/116878#116884 · In reply to: #116883 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 Sent: Monday, January 17, 2022 1:37 PM To: Su, Tao Cc: PHP internals 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. > 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 --- ## #116885 — Dmitry Stogov — 2022-01-17T12:12:19+00:00 URL: https://externals.io/message/116878#116885 · In reply to: #116884 Oh, probably this is just the biggest prime number that fits into a signed 16-bit number :) > 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 > Sent: Monday, January 17, 2022 1:37 PM > To: Su, Tao > Cc: PHP internals > 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. > > > > > […] --- ## #116887 — Larry Garfield — 2022-01-17T17:13:45+00:00 URL: https://externals.io/message/116878#116887 · In reply to: #116885 > 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 > > > > […] --- ## #116889 — tao.su@intel.com — 2022-01-18T01:54:31+00:00 URL: https://externals.io/message/116878#116889 · In reply to: #116885 Interesting! I would like to dig deeper or ask google for more information. I had an impression that I once read a paper about this kind of magic number, but not sure where it was from. @Dmitry Stogov With your permission, if I found anything, I would like to add a few comments into the source code file for records. From: Dmitry Stogov Sent: Monday, January 17, 2022 8:12 PM To: Su, Tao Cc: PHP internals Subject: Re: [PHP-DEV] Reason for ZEND_JIT_COUNTER_INIT set to 32531? Oh, probably this is just the biggest prime number that fits into a signed 16-bit number :) 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 > Sent: Monday, January 17, 2022 1:37 PM To: Su, Tao > Cc: PHP internals > 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. > 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