A call-graph is a relational visualization method. Blackfire profiles are displayed as call-graphs in order to show the caller-callee relation between the function/method calls, which shows best the code's behavior. It enables for instance to understand whether a specific function call is responsible for a bottleneck, or if the bottleneck comes from their parents.
A callee is a function/method which is called by another function/method in your code.
A caller is a function/method which calls another fnction/method in your code.
CPU Time
The CPU Time is a profiling dimension in Blackfire. It corresponds to the time your server's CPU actually spends executing your code.
Exclusive Time
The exclusive time is the time spent by PHP executing a function, excluding the time spent executing its callees. The exclusive time tells you which functions consumed the most time by themselves; those are probably the ones you might want to optimize first.
I/O Time
The I/O time corresponds to the time that the CPU is waiting for input/output operations. That can for instance correspond to network (database calls, Redis calls, HTTP calls, ...) or disk activity (file inclusions, ...). Keep in mind that in Blackfire profiles the I/O is almost never 0 as it also includes non-significant activities like memory access.
Inclusive Time
The unclusive time is the time spent by PHP executing a function, including all of the callees.
A node is a call-graph element. In Blackfire, it represents a function/method call, or an aggregation of calls.
A profile is the data output while measuring the resource consumption of an executed piece of code. In Blackfire, that includes consumption in Wall-time, CPU time, I/O time, Memory, Network, HTTP calls and SQL queries.
The wall time for a function call is the measure of the real time it took for PHP to execute the code. It’s the difference between the time at which PHP entered the function and the time at which PHP left the function. Its is actually the sum of CPU time + I/O time.