Kernel image size and application launch time

Discussion in 'all things UNIX' started by Gullible Jones, Mar 9, 2015.

  1. Gullible Jones

    Gullible Jones Registered Member

    May 16, 2013
    So, this is entirely wall-clock stuff so far, but it's interesting enough that I want to know if anyone has done benchmarks...

    I was experimenting with custom 3.19.1 kernels on a Debian 8 machine, and noticed that there seemed to be some lag when first launching applications with the custom kernel - a lot more lag than with the default one. Launch time for the first lxterminal in an X session was ~1 second with the default kernel, more like 4 seconds with the custom one.

    The main difference seemed to be size. The custom kernel was a 6.5 MB image, with only a few modules. The default was 3.5 MB or so.

    I tried instead compiling a custom kernel with the same config as the Debian default, but other settings (HZ, cgroups, preemption) the same as for the the first custom one. That came out to 2.8 MB. Booted into it, initial lxterminal launch time was back to 1 second.

    Again: wall clock stuff. But: is it possible that an excessively large kernel image has a negative impact on performance? How would that work? Could the kernel be hogging more space in the CPU cache or something, if it's a contiguous image?

    P.S. Google Drive is a great way to store custom kernel packages. :p