How to count the number of guest instructions QEMU executed from the beginning to the end of a run?

Question

I want to benchmark guest instructions per second of QEMU to compare it with other simulators.

How to obtain the guest instruction count? I'm interested both in user and full system mode.

The only solutions I have now would be to log all instructions with either simple trace exec_tb or -d in_asm: How to use QEMU's simple trace backend? and then count the instructions from there. But this would likely considerably reduce simulation performance due to the output operations, so I would likely have to run the test program twice, one with and another without the trace, and hope that both executions are similar (should be, especially for single threaded user mode simulation).

I saw the -icount option, which sounds promising from the name, but when I passed it to QEMU 4.0.0, I didn't see anything happen. Should it print an instruction count somewhere? The following patch appears unmerged and suggests not: https://lists.gnu.org/archive/html/qemu-devel/2015-08/msg01275.html

Answer 1

Basic Profiling

To follow up on Peter's answer, I have recently run into a situation where I wanted to get the instruction count of a program run under QEMU (I'm using v4.2.0, the first where plugins became available).

One of the example plugins, insn.c, does exactly what you want, and returns the count of executed instructions on plugin exit.

(I assume you already know how to run QEMU, so I'll strip this down to the important flags)

qemu-system-arm ... -plugin qemu-install-dir/build/tests/plugin/libinsn.so,arg=inline -d plugin

The first part loads the plugin and passes a single argument, "inline" to it. The next part enables printing of the plugin. You can redirect the plugin output to a different file by adding -D filename to the command line invocation.

More Advanced Profiling

When I was looking for possible ways to profile a program run under QEMU, this is one of the only results of my search that was promising. In the spirit of creating a good record for other searching in the future, here are some links to code that I have written to do just that.

Profiling Plugin code, docs.

_{^{Disclaimer: I wrote the above code.}}