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Date: Thu, 05 Nov 2009 10:58:53 -0800
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To: Arvind Srinivasan <yoarvi@gmail.com>
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Subject: Re: [PHP-DEV] Feedback requested on using #defines to improve the
 performance of  the TSRMG macro
From: christopher.jones@oracle.com (Christopher Jones)


Hi Arvind,

Does the GLOBALS_ID_BASE idea work?  In
"ts_allocate_reserved_id(GLOBALS_ID_BASE+1...)" each extension would
anyway need to reserve an increment to avoid clashes.  Also, why is
GLOBALS_ID_BASE 30 when the largest reserved value is 18?  Maybe I'm
missing something.

Would there be significant memory space or locality issues if one ID
per extension in the PHP source bundle was reserved upfront, even if
those extensions were never enabled?

Chris


Arvind Srinivasan wrote:
 > 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
 >

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