Re: [PATCH] x86/boot: Support uncompressed kernel

[Chao Peng]

On Mon, 2017-03-27 at 15:25 +0200, Arnd Bergmann wrote:
> On Mon, Mar 27, 2017 at 1:47 PM, Michal Marek <mmarek@xxxxxxxx> wrote:
> > 
> > Dne 27.3.2017 v 09:58 Sebastian Andrzej Siewior napsal(a):
> > > 
> > > On 2017-03-24 13:35:40 [+0800], Chao Peng wrote:
> > > > 
> > > > 
> > > > > 
> > > > > > 
> > > > > > > 
> > > > > > > ÂÂÂÂkernelÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂkernel sizeÂÂÂÂtime in
> > > > > > > decompress_kernel
> > > > > > > ÂÂÂÂcompressed (gzip)ÂÂÂÂ3.3MÂÂÂÂÂÂÂÂÂÂÂ53ms
> > > > > > > ÂÂÂÂuncompressedÂÂÂÂÂÂÂÂÂ14MÂÂÂÂÂÂÂÂÂÂÂÂ3ms
> > > > > > 
> > > > Exactly, LZ4 is the fastest. It takes 16ms to complete the
> > > > decompression. Still sounds a little longer when compared to
> > > > uncompressed kernel.
> > > 
> > > Are we seriously talking here about one-time improvement of 13ms
> > > boot time?
> > 
> > If the use case is launching new VM instances continuously, then
> > compressing the kernel image is about as useful as compressing
> > /bin/bash.
> 
> I guess the next step would be to use CONFIG_XIP_KERNEL on x86,
> which requires an uncompressed kernel but has the additional advantage
> of sharing the read-only sections of the kernel image across virtual
> machines, resulting in better RAM and cache usage.

That is something we wanna look into :)

Chao