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Date: Thu, 5 Nov 2009 17:22:34 +0530
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Subject: Feedback requested on using #defines to improve the performance of 
	the TSRMG macro
From: yoarvi@gmail.com (Arvind Srinivasan)

When compiled for multi-threaded (#ifdef ZTS ) operation, the various
subsystems in PHP use dynamically allocated (ts_allocate_id)
identifiers to index into the thread-local storage for each subsystem.
These dynamically allocated ids are used by macros such as CG, EG, PG,
AG.

The TSRMG macro is defined as:
#define TSRMG(id, type, element)	(((type) (*((void ***)
tsrm_ls))[TSRM_UNSHUFFLE_RSRC_ID(id)])->element)

The PG macro is defined as:
# define PG(v) TSRMG(core_globals_id, php_core_globals *, v)

where core_globals_id is
extern PHPAPI int core_globals_id;

cc -E of
	PG(connection_status) = PHP_CONNECTION_ABORTED;
translates to:
 (((php_core_globals *) (*((void ***)
tsrm_ls))[((core_globals_id)-1)])->connection_status) = 1;

and cc -S of the same code results in:
	.loc 1 108 0
	movl	%ebx, %eax
	subl	core_globals_id, %eax
	movl	(%esi), %edx
	sall	$2, %eax
	negl	%eax
	movl	(%edx,%eax), %eax
	movw	$1, 144(%eax)

I used fixed IDs instead of dynamically allocated ones and noticed a
decent improvement in performance (few percentage points) when
running a web-based ecommerce-site workload on SPARC CMT hardware.

With my changes the PG macro is defined as:
# define PG(v) TSRMG(CORE_GLOBALS_ID, php_core_globals *, v)

#define CORE_GLOBALS_ID					10

and core_globals_id is
extern PHPAPI const ts_rsrc_id core_globals_id;

cc -E of the same line of code translates to:
 (((php_core_globals *) (*((void ***)
tsrm_ls))[((10)-1)])->connection_status) = 1;

cc -S (my version):
	.loc 1 108 0
	movl	(%eax), %eax
	movl	36(%eax), %eax
	movw	$1, 144(%eax)

The patch is fairly long, so rather than attach it to this email, i'll
point to it.

It'd be great if someone could give me feedback on my changes -
http://bitbucket.org/arvi/arviq/src/tip/arvi-16-ts_allocate_reserved_id
- for using reserved/fixed IDs for accessing thread-local storage of
frequently used/known/core subsystems. I think the changes only affect
the #ifdef ZTS codepaths.

Thanks,
Arvi