Tideways XHProf Extension

Home of the tideways_xhprof extension - a hierarchical Profiler for PHP.

Looking for tideways Extension to report to tideways.io? Go here. Why did we rename the extension? Blog post here.

This PHP extension is a complete, modernized open-source rewrite of the original XHProf extension, with a new core datastructure and specifically optimized for PHP 7. The result is an XHProf data-format compatible extension with a much reduced overhead in the critical path that you are profiling.

The code for this extension is extracted from the main Tideways extension as we are moving to a new extension with incompatible data-format.

We are committed to provide support for this extension and port it to as many platforms as possible.

Note: The public API is not compatible to previous xhprof extensions and forks, as function names are different. Only the data format is compatible.

About tideways and tideways_xhprof Extensions

This repository now contains an extension by the name of tideways_xhprof, which only contains the XHProf related (Callgraph) Profiler functionality.

Previously the tideways extension contained this functionality together with other functionality used in our Software as a Service.

If you want to use the SaaS, the current approach is to fetch the code using precompiled binaries and packages from our Downloads page.

Requirements

PHP >= 7.0
OS: Linux, MacOS, Windows (Download DLLs)

Installation

You can install the extension from source:

phpize
./configure
make
sudo make install

Configure the extension to load with this PHP INI directive:

extension=tideways_xhprof.so

Restart Apache or PHP-FPM.

Usage

The API is not compatible to previous xhprof extensions and forks, only the data format is compatible:

<?php

tideways_xhprof_enable();

my_application();

file_put_contents(
    sys_get_temp_dir() . DIRECTORY_SEPARATOR . uniqid() . '.myapplication.xhprof',
    serialize(tideways_xhprof_disable())
);

By default only wall clock time is measured, you can enable there additional metrics passing the $flags bitmask to tideways_xhprof_enable:

<?php

tideways_xhprof_enable(TIDEWAYS_XHPROF_FLAGS_MEMORY | TIDEWAYS_XHPROF_FLAGS_CPU);

my_application();

file_put_contents(
    sys_get_temp_dir() . DIRECTORY_SEPARATOR . uniqid() . '.myapplication.xhprof',
    serialize(tideways_xhprof_disable())
);

Data-Format

The XHProf data format records performance data for each parent => child function call that was made between the calls to tideways_xhprof_enable and tideways_xhprof_disable. It is formatted as an array with the parent and child function names as a key concatenated with ==> and an array value with 2 to 5 entries:

wt The summary wall time of all calls of this parent ==> child function pair.
ct The number of calls between this parent ==> child function pair.
cpu The cpu cycle time of all calls of thi sparent ==> child function pair.
mu The sum of increase in memory_get_usage for this parent ==> child function pair.
pmu The sum of increase in memory_get_peak_usage for this parent ==> child function pair.

When TIDEWAYS_XHPROF_FLAGS_MEMORY_ALLOC flag is set, the following additional values are set:

mem.na The sum of the number of all allocations in this function.
mem.nf The sum of the number of all frees in this function.
mem.aa The amount of allocated memory.

If TIDEWAYS_XHPROF_FLAGS_MEMORY_ALLOC_AS_MU is set, TIDEWAYS_XHPROF_FLAGS_MEMORY_ALLOC is activated and, if TIDEWAYS_XHPROF_FLAGS_MEMORY_MU is not set, mem.aa is additionally returned in mu.

There is a "magic" function call called "main()" that represents the entry into the profiling. The wall time on this performance data describes the full timeframe that the profiling ran.

Example:

<?php

array(
    "main()" => array(
        "wt" => 1000,
        "ct" => 1,
        "cpu" => 400,
    ),
    "main()==>foo" => array(
        "wt" => 500,
        "ct" => 2,
        "cpu" => 200,
    ),
    "foo==>bar" => array(
        "wt" => 200,
        "ct" => 10,
        "cpu" => 100,
    ),
)

Clock Sources

Any Profiler needs timer functions to calculate the duration of a function call and the tideways_xhprof extension is no different. On Linux you can collect timing information through various means. The classic, most simple one is the function gettimeofday, which PHP uses when you call microtime(). This function is slower compared to other mechanisms that the kernel provides:

clock_gettime(CLOCK_MONOTONIC) returns a monotonically increasing number (not a timestamp) at very high precision and much faster than gettimeofday(). It is the preferred and recommended API to get high precision timestamps. On Xen based virtualizations (such as AWS) this call is much slower than on bare-metal or other virtualizations (Blog post)
TSC (Time Stamp Counter) API is accessible in C using inline assembler. It was the timing API that the original XHProf extension used and it is generally very fast, however depending on the make and generation of the CPU might not be synchronized between cores. On modern CPUs it is usually good to use without having to force the current process to a specific CPU.

Tideways on Linux defaults to using clock_gettime(CLOCK_MONOTONIC), but if you are running on Xen based virtualization, you could try to reduce the overhead by setting `tideways.clock_use_rdtsc=1" in your PHP.ini.