Reducing initramfs size and speed up the generation

[Benjamin Drung]

On Thu, 2023-07-13 at 08:32 +0100, TJ wrote:
> Is there a specific reason why the focus is on trying to shoe-horn 
> everything possible into the initrd.img and then compress rather than 
> winnow out the files an installed system will never need to find the 
> root file-system?

These are two orthogonal targets. MODULES=most is the default, because
you can change the hardware and the system will still boot. Advanced
users can use MODULES=dep to only include the needed bits, but then they
have to be aware of it when changing the hardware. Improving the way we
compress the initramfs could help in both configurations.

> I tackled the issue of ever-expanding host-generated initrd.img file 
> sizes when they began hitting 80MB+ back in 2018 and since then have 
> carried my own patches that reduce sizes by not including files the host 
> will not need.
> 
> One small change that brings major benefits is only including the 
> firmware files required, not every file declared by a kernel module. The 
> GPU drivers are the main culprit there with amdgpu declaring over 500 of 
> which, for any individual GPU, only a handful are relevant, but 
> Plymouth's pulling in multiple GPU drivers doesn't help that.
> 
> Statistics (initrd.img with kernel v6.2.4):
> MODULES=  FIRMWARE_LOADED size      MOST DEP firmwares build-time
> most      false           77117694           634       14.49
> most      true            60302859 -22%        8       11.99
> dep       false           42489938 -45%      606       6.84
> dep       true            25704125 -66% -40%   8       6.35
> 
> FIMWARE_LOADED=true relies on a simple kernel patch which I've been 
> meaning to upstream that writes "Firmware loaded: <file>" for each.
> 
> $ journalctl --dmesg | grep 'Firmware loaded' | head -n 15
> Jul 02 11:42:21 sunny kernel: firmware_class: Firmware loaded: reporting
> Jul 02 11:42:21 sunny kernel: radeon 0000:0a:00.0: Firmware loaded: 
> radeon/verde_pfp.bin
> Jul 02 11:42:21 sunny kernel: radeon 0000:0a:00.0: Firmware loaded: 
> radeon/verde_me.bin
> Jul 02 11:42:21 sunny kernel: radeon 0000:0a:00.0: Firmware loaded: 
> radeon/verde_ce.bin
> Jul 02 11:42:21 sunny kernel: radeon 0000:0a:00.0: Firmware loaded: 
> radeon/verde_rlc.bin
> Jul 02 11:42:21 sunny kernel: radeon 0000:0a:00.0: Firmware loaded: 
> radeon/verde_mc.bin
> Jul 02 11:42:21 sunny kernel: radeon 0000:0a:00.0: Firmware loaded: 
> radeon/verde_smc.bin
> Jul 02 11:42:21 sunny kernel: radeon 0000:0a:00.0: Firmware loaded: 
> radeon/TAHITI_uvd.bin
> Jul 02 11:42:21 sunny kernel: radeon 0000:0a:00.0: Firmware loaded: 
> radeon/TAHITI_vce.bin
> Jul 02 11:42:22 sunny kernel: r8152 2-8.3:1.0: Firmware loaded: 
> rtl_nic/rtl8153a-4.fw
> Jul 02 11:42:28 sunny kernel: platform regulatory.0: Firmware loaded: 
> regulatory.db
> Jul 02 11:42:28 sunny kernel: platform regulatory.0: Firmware loaded: 
> regulatory.db.p7s
> 
> My experiments and patches are documented at
> 
> https://iam.tj/projects/ubuntu/initramfs-tools/

That is a really good idea. After looking at the patches, the options 1
and 2 (sysfs or procfs interface) are the more robust ones (but need
more work implementing them in the kernel). Option 3 (kernel logging)
seem to be too fragile for using it programmatically. What happens if a
user boot with quiet option and clears the kernel log buffer?

Is introducing FIRMWARE_LOADED really needed? Isn't it enough to only
include the loaded firmware for MODULES=dep and all firmware otherwise?

> The main take is the question:
> 
> Is MODULES=most really the best default for installed-on-host images (it 
> obviously is for installer and portable images). If it can be nuanced 
> then =DEP plus winnowing the firmware files gives great gains with 
> minimal effort.

MODULES=most is the best default since it allows changing the underlying
hardware.

-- 
Benjamin Drung
Debian & Ubuntu Developer