Hi!
If I read the history correctly, then I see the following changes to code:
In 2005 a loop reading child process' (dpkg) output was added, together
with a call to usleep(1000) that slows an idle loop down. This was made
in https://salsa.debian.org/apt-team/apt/-/commit/75ef8f1417.
In 2006 this bug was reported.
In 2007 a call to select() was added in the loop to postpone read()
calls until more data from the child process is available. This was made
in https://salsa.debian.org/apt-team/apt/-/commit/090c656632. Notice
that select() was later replaced with pselect().
Also in 2007 the call to usleep() call in the loop was finally removed.
This was done in https://salsa.debian.org/apt-team/apt/-/commit/7fdafa0f34.
I didn't run reporter's test with powertop before 090c656632 or after
7fdafa0f34 so I don't know if/how much the problem was reduced. It would
be kind of difficult for me to install Debian's version from 2006 to
reproduce the issue in the original apt version.
Kamil
