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Estimate emerge time

You can analyze your system's emerge.log file to find out how long a given package took to compile and also to estimate the time of future compile jobs, or you can use genlop, which is designed for the job.

Code Listing 4.1: Example of how it works:
# genlop -nt kdelibs
Tue May 8 18:26:59 2007 >>> kde-base/kdelibs-3.5.6-r8
merge time: 38 minutes and 6 seconds.

This information can be used to estimate how long an update would take. The tool can be used to calculate the emerge time for a variety of package sets, like a world update, by calling it this way:

Code Listing 4.2: Example of emerging world:
# emerge -uDp world | genlop -p
These are the pretended packages: (this may take a while; wait...)
[ebuild U ] app-office/openoffice-2.2.1 [2.2.0]
[ebuild U ] media-libs/netpbm-10.39.0 [10.37.0]
Estimated update time: 5 hours, 50 minutes.

Now, what if you have a new package that you didn't have installed, such as you want to install fluxbox on a machine that previously did not have X installed:

Code Listing 4.3: Example of using on a new package:
# emerge -p fluxbox | genlop -p
...
[ebuild N ] x11-libs/libXmu-1.0.3 USE="-debug -ipv6"
[ebuild N ] x11-apps/xmessage-1.0.1 USE="-debug -xprnt"
...
!!! Error: couldn't get previous merge of xmessage; skipping...
!!! Error: couldn't get previous merge of fluxbox; skipping...
...
!!! Error: fluxbox never merged; estimated time unknown.

Genlop will only reference the packages it knows. If you use the -q option (genlop version >= 0.30.7), an online database running on gentoo.linuxhowtos.org is queried for compile times based on users with an identical CPU to yours.

Code Listing 4.4: Above query results in:
# emerge -p fluxbox | genlop -p -q
These are the pretended packages: (this may take a while; wait...) ...
Estimated update time: 38 minutes.

The times are not 100% accurate; it does not respect USE flags or memory speed, hard disk speed, or other factors. However, as the times get averaged over different users, these factors become less important.