Re: [PATCH RFC] x86: Add CONFIG_KERNEL_UNCOMPRESSED support

[Ingo Molnar <mingo@kernel.org>]

* Ard Biesheuvel <ardb@kernel.org> wrote:

> > But I wasn't sure how to wire that up in a nice way. I guess the 
> > nicest option would be to create a separate kconfig variable for 
> > the compression level to use for any cmd_lz4/cmd_lz4_with_size 
> > invocations in the build process; and then maybe only make this 
> > option visible if LZ4 is selected as kernel compression method?
> >
> > Another option would be to create a new option in the "Kernel 
> > compression mode" choice menu with a name like "LZ4 (fast)", turn 
> > CONFIG_KERNEL_LZ4 into an internal flag that is selected by both 
> > LZ4 variants shown in the choice menu, and duplicate some of the 
> > make rules, but that seems overly complicated.
> >
> 
> I didn't realise that KERNEL_UNCOMPRESSED already exists and you are 
> just wiring it up for x86. But I still think that we should avoid 
> that, not only because it is yet another bzImage format but also 
> because I still see a 3x size reduction even with the fastest 
> setting.
> 
> I think adding one Kconfig symbol that depends on KERNEL_LZ4 and 
> switches from -9 to -1 for LZ4 only is reasonable.

Maybe a CONFIG_COMPRESS_FAST option that maps to and enables the 
current fastest compressor? Then we can also add LZ4_FAST and map it to 
it. (And if a future fastest compressor is added it can change this 
mapping.) Or something like that?

And if there's still a measurable difference in total build time (say 
larger than 1%) from doing it all uncompressed, then I think we should 
go with Jann's original patch that hooks up zero-compression on x86. It 
doesn't look overly complicated.

Thanks,

	Ingo