kernel build time and size data (comparison of esstra with non-esstra builds)

[tbird20d]

Here is some data from my tests performing Linux kernel builds with esstra.

My machine is a Dell desktop (x86_64), with 16 cores, 32G RAM, and 188G of open space on a 1.8T drive.
I was building just the statically linked kernel binary image (vmlinux), without building modules.
I used the config for my desktop machine, derived from the default Ubuntu 24.04 x86_64 config.

A kernel build without esstra installed takes:
1st run:
real 10m59.139s
user 110m50.858s
2nd run:
real 11m4.708s
user 110m52.484s
3rd run:
real 11m0.665s
user 110m55.890s

Average:
real 11M1s (661s)
user 110m53s (6603s)

A kernel build with esstra installed took:
1st run:
real 12m29.011s
user 114m21.491s
2nd run:
real 11m53.083s
user 114m50.584s
3rd run:
real 11m48.747s
user 114m46.115s

Average:
real 12m3s (723s)
user 114m39 (6879s)

Kernel build overhead was approximately:
9.4% real time
4.2% cpu time (in user space)

For output file size that included esstra data, I got the following numbers:
(all sizes in bytes, unless shown otherwise with a suffix)

without esstra data:
- vmlinux: 453,766,632 (453M)
- arch/x86/boot/compressed/vmlinux: 14,100,280
- arch/x86/boot/compresses/vmlinux.bin: 56,626,008
- arch/x86/boot/compresses/vmlinux.bin.zst: 13,835,528
- arch/x86_64/boot/bzImage: 14,524,607

with esstra data:
- vmlinux: 766,636,328 bytes (766M)
- arch/x86/boot/compressed/vmlinux: 16,189,240
- arch/x86/boot/compresses/vmlinux.bin: 369,495,688
- arch/x86/boot/compresses/vmlinux.bin.zst: 14,453,836
- arch/x86/boot/bzImage: 16,613,567

The size of the extracted esstra data (in raw format) for vmlinux was:
vmlinux.esstra-data: 155583207

There's an approximately 310M difference in size between vmlinux without esstra
data and the vmlinux with esstra data. That's suspiciously close to 2 times the
size of the esstra data. I haven't looked at the actual ELF layout to see what the
remaining approximately 156M of difference in size is. (Possibly a duplicate
.esstra section, or some other hole that is .esstra-sized, but I need to check).

I hope this data is useful

[NamaeTakuya]

Hello @tbird20d -san,

Thank you for sharing this detailed test data — very helpful.
We’ll run similar measurements on our side as well.
Regarding the .esstra section size: we are currently collecting size metrics across various OSS projects and plan to publish a report soon under doc/case-study/.
For the point about the ~310MB delta vs. ~155MB raw ESSTRA data: please try the esstra shrink command (https://github.com/sony/esstra/blob/main/util/README.md#command-shrink), e.g.:

$ esstra shrink vmlinux

This removes duplication in metadata and significantly reduces the binary size.
Alternatively, you can use ESSTRA Link (https://github.com/sony/esstra/blob/main/link/README.md) to eliminate duplication during the build rather than post-build.