Hi,
I've added the corresponding patch for APC, so anyone is able to verify
the performance difference.
http://wiki.php.net/rfc/performanceimprovements
Thanks. Dmitry.
Dmitry Stogov wrote:
Hi,
I've published all the patches, their description and performance
evaluation at http://wiki.php.net/rfc/performanceimprovements
In two words the patches give 0-20% improvement even on real-life
applications.
I'm going to commit them into trunk in a week in case of no objections.
Of course, they are binary incompatible. Some extensions (especially VM
depended e.g. APC, xdebug, etc) will have to be modified to support the
changes.
Thanks. Dmitry.
Zeev Suraski wrote:
Hi,
Over the last few weeks we've been working on several ideas we had for
performance enhancements. We've managed to make some good progress.
Our initial tests show roughly 10% speed improvement on real world
apps. On pure OO code we're seeing as much as 25% improvement (!)
While this still is a work in progress (and not production quality
code yet) we want to get feedback sooner rather than later. The diff
(available at http://bit.ly/aDPTmv) applies cleanly to trunk. We'd be
happy for people to try it out and send comments.
What does it contain?
1) Constant operands have been moved from being embedded within the
opcodes into a separate literal table. In additional to the zval it
contains pre-calculated hash values for string literals. As result PHP
uses less memory and doesn't have to recalculate hash values for
constants at run-time.
2) Lazy HashTable buckets allocation – we now only allocate the
buckets array when we actually insert data into the hash for the first
time. This saves both memory and time as many hash tables do not have
any data in them.
3) Interned strings (see
<http://en.wikipedia.org/wiki/String_interning>http://en.wikipedia.org/wiki/String_interning).
Most strings known at compile-time are allocated in a single copy with
some additional information (pre-calculated hash value, etc.). We try
to make most incarnations of a given string point to that same single
version, allowing us to save memory, but more importantly - run
comparisons by comparing pointers instead of comparing strings and
avoid redundant hash value calculations.
A couple of notes:
a. Not all of the strings are interned - which means that if a
pointer comparison fails, we still go through a string comparison;
But if it succeeds - it's good enough.
b. We'd need to add support for this in the bytecode caches. We'd be
happy to work with the various bytecode cache teams to guide how to
implement support so that you do not have to intern on each request.
To get a better feel for what interning actually does, consider the
following examples:
// Lookup for $arr will not calculate a hash value, and will only
require a pointer comparison in most cases
// Lookup for "foo" in $arr will not calculate a hash value, and will
only require a pointer comparison
// The string "foo" will not have to be allocated as a key in the Bucket
// "blah" when assigned doesn't have to be duplicated
$arr[“foo”] = “blah”;
$a = “b”;
if ($a == “b”) { // pointer comparison only
...
}
Comments welcome!
Zeev
Patch available at: http://bit.ly/aDPTmv
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