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To: "PHP Development" <internals@lists.php.net>
Date: Sun, 17 Aug 2008 04:19:10 +0200
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Message-ID: <200808170419.11153.arnaud.lb@gmail.com>
Subject: [PATCH] ZTS as fast as non-ZTS
From: arnaud.lb@gmail.com (Arnaud Le Blanc)

Hi,

Currently the way globals work forces to pass a thread-local-storage pointer 
across function calls, which involves some overhead. Also, not all functions 
get the pointer as argument and need to use TSRMLS_FETCH(), which is slow. For 
instance emalloc() involves a TSRMLS_FETCH(). An other overhead is accessing 
globals, using multiple pointers in different locations.

The following patch caches each global address in a native TLS variable so 
that accessing a global is as simple as global_name->member. This removes the 
requirement of passing the tls pointer across function calls, so that the two 
major overheads of ZTS builds are avoided.

Globals can optionally be declared statically, which speeds up things a bit.

Results in bench.php:
non-ZTS:						3.7s
ZTS unpatched:					5.2s
ZTS patched:					4.0s
ZTS patched and static globals:	3.8s

The patch introduces two new macros: TSRMG_D() (declare) and TSRMG_DH() 
(declare, for headers) to declare globals, instead of the current "ts_rsrc_id 
foo_global_id". These macros declare the global id, plus the __thread pointer 
to the global storage.

ts_allocate_id now takes one more callback function as argument to bind the 
global pointer to its storage. This callback is declared in TSRMG_D[H]().

As all TSRMLS_* macros now does nothing, it is needed to call ts_resource(0) 
explicitly at least one time in each thread to initialize its storage. A new 
TSRMLS_INIT() macro as been added for this purpose.

All this is disabled by default. --with-tsrm-__thread-tls enables the features 
of the patch, and --with-tsrm-full-__thread-tls enables static declaration of 
globals.

It as been tested on Linux compiled with --disable-all in CLI and a bit in 
Apache2 with the worker MPM. Known issues: 
- Declaring globals statically (--with-tsrm-full-__thread-tls) causes troubles 
to dlopen(), actually Apache wont load the module at runtime (it works with 
just --with-tsrm-__thread-tls).
- The patch assumes that all resources are ts_allocate_id()'ed before any 
other thread calls ts_allocate_id or ts_resource_ex(), which is possibly not 
the case.

The patch needs some tweaks and does not pretend to be included in any branch, 
but I would like to have some comments on it.

The patch: http://arnaud.lb.s3.amazonaws.com/__thread-tls.patch

Regards,

Arnaud