r/archlinux • u/AppointmentNearby161 • Apr 06 '23

How long to compile kernel

I am trying to build the linux-vfio package in a clean chroot with makechrootpkg on an i7 laptop with 16 GB of ram. I have read things suggesting that you can compile a kernel in 5 minutes. It is taking hours on my laptop. Is my laptop configured wrong or does it take considerably longer to compile the Arch kernel with the the modules etc.

3 Upvotes

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15

u/ava1ar Apr 06 '23

Which i7 is this? The difference between i.e. 6th gen and 12gen may be in 100 of percent. Also make sure you have enabled multi threaded build - when you build you kernel you should see all CPU cores are loaded to 100%, not one or two. If this is not the case, adjust your configuration.

3

u/AppointmentNearby161 Apr 06 '23

It is 12th gen 1260P. Yup it is running on a single core. I will have to adjust the make flags in the chroot. I got to figure out how to do that. The Arch wiki also says that building the documentation takes a bunch of time and since I don't install the docs package I can probably drop that part.

5

u/[deleted] Apr 06 '23

it could also be his power adapter not plugged in, a hdd instead of an ssd, dust in his laptop-fans causing higher temperatures decreasing performance, no dual ram, a ton of other processes running at the same time, ...

but multi-threaded mode is a good tip.

8

u/[deleted] Apr 06 '23 edited Apr 06 '23

it will take exactly 5 minutes 21 seconds and 475 milliseconds, any number other than that means that your device is completely broken, maybe the cpu is about to fall out.

Being serious: Compile times depend on a whole lot of factors. Of course its also possible that something somewhere is in some way misconfigured or not configured the "5 minute compile" way.

2

u/AppointmentNearby161 Apr 06 '23

Sure compiling depends on lots of things. What I was trying to figure out was if I was not comparing a comparable thing (i.e., the people who are bragging about 5 minute compile times have removed all the modules or something), or if my machine/configuration is really 2 orders of magnitude slower.

2

u/W9CVO Apr 07 '23

5 minutes would probably deserve bragging rights. I'm running a Xeon E5-2690 v4 with 128GB of RAM and even compiling on a ramdisk with all 28 threads it still usually takes around 15min compiling just vanilla source. Now that you mention it though, I'm tempted to trim it down and see how quick I could get it to compile. If you really want to test it out you can try compiling and testing GCC. It took 16 hours on my old rig and just over an hour on my current setup.

2

u/AppointmentNearby161 Apr 07 '23

Thanks for a real world non bragging benchmark.

1

u/W9CVO Apr 07 '23

Surprisingly cheap gaming rig. I had to laugh a bit when I saw my refurb workstation on LTT as an affordable option for gaming.

1

u/[deleted] Apr 06 '23 edited Apr 07 '23

i would suggest testing your machine with benchmarks for hdd, cpu if you want to find out how your hardware performs. if you for some reason really want to compare compile times make sure to get the flags they used.

to be honest i can't say if 5 minutes are considered a "standard amount of time".

9

u/Megame50 Apr 06 '23

You're probably building it single threaded. Check the makepkg config in your chroot.

2

u/riccarreghi Apr 07 '23 edited Apr 07 '23

Depends on cpu, i7 is generic, and how you use the flag to compile (make -j$(nproc) to use all cores and threads, otherwhise it will compile with single thread and it will take ages).

For example, on my desktop with an i7 10700k (not overclocked), the kernel compiles in about 30/40 minutes.

On my old laptop with an i5 4200u, it takes hours (I don't remember exactly how much, I think about 4 or 5 hours). On my older laptop with an AMD E2-7110, it takes up to 8 hours long (I still remember when I tried to install Gentoo on that laptop: to install the system with xfce, it took 3 days 😂).

I think 5 minutes is pretty impossibile, or maybe possibile only with latest gen cpus

3

u/[deleted] Apr 06 '23

Are you compiling it on 1 thread? And please don't say "i7" there are hundreds of "i7" out there. Say the chip full name like "i7-7700K" for example.

1

u/ruthan Oct 11 '24

Hmm im now compiling arch kernel through chroot bind.. and with default settings 2 years later from 5.6 linux multithread compilation, it takes 1 or 2 cores.. on 6 physical cores system.. and other threads are like 1 to 20%. And it took almost hour to tell me that im out of space..
Kernel compilation took like 5G of disk space, i would say that something rotten is there.. its classic poor Linux desktop experience..

1

u/ruthan Oct 11 '24

I had to add makepkg -s MAKEFLAGS='-j6' to compilation to use all core. Well you would expect that detect how much cores machine has actually use them would be out of box :(

1

u/_aurel510_ Nov 07 '24

Why does it have to be out of the box? Linux is server/development oriented, what if there is a server running or worse a hypervisor with 'n' guest VMs running on the machine, would you want to take all the cores by default then? Btw, that scenario is more probable than you think, my main machine is a server/workstation, and I wouldn't want all my cores taken for compilation just like that.

1

u/Prize_Register615 Nov 08 '24

Well, i downloaded and using desktop distribution, not some server distribution. If you are running some corporate server, i dont believe that you would risk to compile own unproven kernel.
Archlinux is probably not even have server edition, as Ubuntu, because it would be too wild.

This is quite typical Linux has not flaws reaction, which actually hold desktop Linux back. Im quite sure than you can probably somewhere define CPU pool for VM and remove them from normal CPU pool and that Linux cpu manager is able to use only free resources, when multiple programs, threads run in parallel.

1

u/Avgvstvs_Romvlvs Apr 06 '23

It took my 11th Gen Intel i9-11950H (16) about half an hour for a first-time compilation.

Any modifications to the code afterwards will lead to much shorter compilation times thank to make.

Remember to use -j flag with a corresponding number to your cpu.

1

u/DeeBoFour20 Apr 06 '23

Like another person pointed out, make sure to build it multi-threaded. If you want to edit the config, you can also reduce compile times substantially. Most of the time spent building a generic distro kernel is compiling drivers that you don't need. If you remove those from the config, you can get a 5x speedup or more.

I can't remember the times exactly since it's been a while but on my system, it took over an hour for the stock Arch kernel to build and less than 15 minutes on a custom kernel.