Hi Richard, Helen, On Sat, Nov 3, 2018 at 4:10 AM Richard Weinberger <richard@xxxxxx> wrote: > > Helen, > > Am Samstag, 3. November 2018, 04:53:39 CET schrieb Helen Koike: > > As mentioned in the discussion from the previous version of this patch, Android > > and Chrome OS do not use initramfs mostly due to boot time and size liability. > > Do you have numbers on that? Originally, we saved ~200 ms, but I don't think we have recent numbers. (Unless Helen has some!) We first authored and posted this patch in 2010: - https://marc.info/?l=dm-devel&m=127429492521964&w=2 - https://marc.info/?l=dm-devel&m=127429499422096&w=2 - https://marc.info/?l=dm-devel&m=127429493922000&w=2 Every Chrome OS device uses a variant of this patch as well as Android devices starting last year (if they use AVB 2.0). Originally, the intent was the measured latency reduction. We get a linear speed improvement when doing a cryptographic verification of the kernel and initramfs. Why? More data == more hashes (sha256 w/compute per block). There's additional overhead from bringing up early userspace, but those are the numbers I don't have. > I understand that using something like dracut with systemd inside is not what you > want from a boot time point of view. > But having an initramfs embedded into the kernel image which contains only a single > static linked binary can be *very* small and fast. > If you invest a little more time, you don't even need a libc, just fire up some > syscalls to setup your dm. I use this technique regularly on deeply embedded systems > to setup non-trivial UBIFS/crypto stuff. > > Want I'm trying to say, before adding ad-hoc a feature to the kernel, we should be > very sure that there is no other way to solve this in a sane manner. > We have initramfs support for reasons. I very much appreciate the perspective, but after 8 years in shipping devices after integrating feedback from kernel maintainers over the subsequent years, this doesn't feel like an "ad-hoc" feature. It's been effective and fit in well with the existing kernel functionality, etc (imho :). What level of performance improvement or other changes might be necessary to make the cut? Thanks! will
