Kernel Compilation Times

David S. Miller complains that CONFIG_MODULE_SIG slows down builds, and he does hundreds of allmodconfig builds every day.

This complaint falls apart fairly quickly in the comments; he knows he can simply turn it off, but what about others who he simply tells to test with allmodconfig?  One presumes they are not doing hundreds of kernel builds a day.

linux-next had the same issue, and a similar complaint; I had less sympathy when I suggested they might want to also turn off CONFIG_DEBUG_INFO if they were worried about compile speed, and indeed, found out Stephen already did.  Now they turn off CONFIG_MODULE_SIG, too.

Here are some compile times on my i386 laptop, using v3.7-rc1-1-g854e98a as I turn options off:

  • allmodconfig: 52 minutes
  • … without CONFIG_MODULE_SIG: 45 minutes
  • … without CONFIG_DEBUG_INFO: 40 minutes
  • … without CONFIG_KALLSYMS: 37 minutes
  • … using -O1 instead of -Os: 24 minutes (not a good idea, since we lose CONFIG_DEBUG_STRICT_USER_COPY_CHECKS).

In summary, the real problem is that people don’t really want ‘allmodconfig’.  They want something which would compile a kernel with as much coverage as possible with no intention of actually booting it; say ‘allfastconfig’?

Latinoware 2012

I’m keynoting at in Brazil in two weeks (assuming I get my visa in time! ).  Looking forward to my first trip to South America as well as delivering a remix of some of my favourite general hacking talks. And of course, catching up with maddog!

What Can I Do To Help?

Enthusiasm is a shockingly rare resource, anywhere. The reason enthusiasm is a rare resource is because it’s fragile; I’ve seen potentially-great ideas abandoned because the initial response was a liturgy of reasons why it won’t work.  It’s not the criticism which kills, it’s the scorn.

So when someone emails or approaches you with something they’re excited about, please reply thinking “What can I do to help?”  Often I just provide an encouraging and thoughtful response: a perfectly acceptable minimum commitment.  If you offer pointers or advice, take extra care to fan that delicate flutter of enthusiasm without extinguishing it. Other forces will usually take care of that soon enough, but let it not be you.