After profiling a Java (or other supported VM) application, the
OProfile JIT support creates ELF binaries from the
intermediate files that were written by the agent library.
The ELF binaries are named <tgid>.jo.
With the symbol information stored in these ELF files, it is
possible to map samples to the appropriate symbols.
The usual analysis tools (opreport and/or opannotate) can now be used to get symbols and assembly code for the instrumented VM processes.
Below is an example of a profile report of a Java application that has been instrumented with the provided agent library.
$ opreport -l /usr/lib/jvm/jre-1.5.0-ibm/bin/java CPU: Core Solo / Duo, speed 2167 MHz (estimated) Counted CPU_CLK_UNHALTED events (Unhalted clock cycles) with a unit mask of 0x00 (Unhalted core cycles) count 100000 samples % image name symbol name 186020 50.0523 no-vmlinux no-vmlinux (no symbols) 34333 9.2380 7635.jo java void test.f1() 19022 5.1182 libc-2.5.so libc-2.5.so _IO_file_xsputn@@GLIBC_2.1 18762 5.0483 libc-2.5.so libc-2.5.so vfprintf 16408 4.4149 7635.jo java void test$HelloThread.run() 16250 4.3724 7635.jo java void test$test_1.f2(int) 15303 4.1176 7635.jo java void test.f2(int, int) 13252 3.5657 7635.jo java void test.f2(int) 5165 1.3897 7635.jo java void test.f4() 955 0.2570 7635.jo java void test$HelloThread.run()~ |
Depending on the JVM that is used, certain options of opreport and opannotate do NOT work since they rely on debug information (e.g. source code line number) that is not always available. The Sun JVM does provide the necessary debug information via the JVMTI[PI] interface, but other JVMs do not.
As you can see in the opreport output, the JIT support agent for Java
generates symbols to include the class and method signature.
A symbol with the suffix ˜<n> (e.g.
void test$HelloThread.run()˜1) means that this is
the <n>th occurrence of the identical name. This happens if a method is re-JITed.
A symbol with the suffix %<n>, means that the address space of this symbol
was reused during the sample session (see Section 6, “Overlapping symbols in JITed code”).
The value <n> is the percentage of time that this symbol/code was present in
relation to the total lifetime of all overlapping other symbols. A symbol of the form
<return_val> <class_name>$<method_sig> denotes an
inner class.