I've seen this statement before about the impact of caching the actual
compilation (or mere tokenization?) to bytecode being very small
compared to the impact of avoiding disk access. I am curious if there
are any measurements breaking this down. Read-only access to code in
files already buffered by the OS (not files read for the first time)
ought to be very fast.
On Tue, May 22, 2012 at 11:00 AM, Richard Lynch <c...@l-i-e.com> wrote:
> On Wed, May 9, 2012 5:05 pm, Xin Tong wrote:
>
>> I am new to php runtime. i am doing some research on runtime
>> interpreter. can anyone please tell me where the interpreter of the
>> php runtime is ? which file ? and does the php runtime has a JIT
>> compiler ?
>
> I believe the interpreter is built out of bison/yacc files, so you
> could start with those to find out where they put it.
>
> The php runtime is a JIT parser/compiler to a bytecode, which is then
> run by the Zend Engine (see above).
>
> Actually, that last statement might imply the the zend directory would
> also be a good place to look.
>
> Finally, it should be noted that APC and other caching mechanisms save
> a great deal of time by not hitting the disk to load the script, but
> keeping it in RAM, if possible.
>
> As "gravy" on top of that, the bytecode is saved in cache instead of
> source, so it is not a JIT if one of those caches is in use.
>
> Psuedo code to describe the difference the APC (or other cache) makes:
>
>
> //save hitting the hard disk
> if ( $source_code = in_cache($path)){
> }
> else{
> //super-duper slow!!!
> $source_code = file_get_contents($path);
> }
> $bytecode = zend_parse($source_code);
> zend_execute($bytecode);
>
> //save hitting the hard disk
> //and a small bonus, cache the bytecode, not source:
>
> if ($bytecode = in_cache($path)){
> //do nothing
> }
> else{
> $source_code = file_get_contents($path);
> $bytecode = zend_parse($source_code);
> }
> zend_execute($bytecode);
>
>
> The savings from parsing is chump change compared to disk I/O.
>
> It's also trivial chump change to implement.
>
> Ever ounce counts :-)
>
> --
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> http://richardlynch.blogspot.com/search/label/brain%20tumor
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>
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