How measure boot time?

I only use qemu several time, so I am really newbie to qemu virtualization (but I am experience in using linux for several years). In linux, I know I can measure a command by time command. However, when I boot up an image using qemu-system-x86_64, how do I know how long qemu takes to boot the image until e.g. login screen gets display (or to boot a specific process)?

The information I find so far is https://stefano-garzarella.github.io...nux-boot-time/. But this looks like patching linux and qemu from source code. So I am curious is there any way to measure such metrics (boot time) without applying patch? For instance a flag in qemu command can be used to measure or monitor such info.

Qemu I use is version 4.1.0. Linux kernel version 5.2.0-2-amd64

Why?

By that I mean, why do you want to measure boot time, and what are the criteria? It helps to know what you REALLY want to measure and why before suggesting an answer.

Any distro's boot time can be measured from within the distro, whether it's in a VM or not.
With systemd distros, the command is

systemd-analyze

(OK, strictly speaking that measures boot time from the moment init starts, not before)

Update:
I managed to install kernel source 5.4 by apt-get source linux-source-5.4. And set PERF_EXEC_PATH to /path/to/linux-source-5.4/tools/perf. But the result is the same (no qemu_init_end error is still thrown).


Thanks for all the reply. I come across to https://github.com/stefano-garzarella/qemu-boot-time It looks like what I need. So I run the command based on How to use section by replacing qemu command I use. Then it generates qemu_perf.data. However when I try the command at [code]Example of output[/b]

perf script -s qemu-boot-time/perf-script/qemu-perf-script.py -i qemu_perf.data

It throws the following error message.

in trace_begin
Traceback (most recent call last):
  File "qemu-boot-time/perf-script/qemu-perf-script.py", line 195, in kvm__kvm_entry
    if (events.traces[pid].qemu_init_end != 0):
AttributeError: 'collections.defaultdict' object has no attribute 'qemu_init_end'
Fatal Python error: problem in Python trace event handler

It seems to me the problem stems from the qemu-perf-script.py line 125 (https://github.com/stefano-garzarell...script.py#L125) because it uses autodict() which default do not have qemu_init_end (but I could be wrong). However, when search packages with pip, pip3, or apt-cache I don't find any related packages e.g. pip3 search autodict, apt-cache search autodict. What packages should I install to fix this issue? Or any thing/ code that I should add in order to fix this (I haven't use autodict() so I am not sure how that works or any docs linking to that lib)?

Thanks for help