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

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Date:   Fri, 24 Mar 2017 00:31:17 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Yinghai Lu <yinghai@...nel.org>
Cc:     Chao Peng <chao.p.peng@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Michal Marek <mmarek@...e.com>,
        Kees Cook <keescook@...omium.org>, Baoquan He <bhe@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Paul Bolle <pebolle@...cali.nl>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Borislav Petkov <bp@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>, Petr Mladek <pmladek@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Tejun Heo <tj@...nel.org>, Daniel Mack <daniel@...que.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Helge Deller <deller@....de>, Rik van Riel <riel@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH] x86/boot: Support uncompressed kernel

On (03/23/17 08:07), Yinghai Lu wrote:
> On Thu, Mar 23, 2017 at 5:51 AM, Chao Peng <chao.p.peng@...ux.intel.com> wrote:
> > Compressed kernel has its own drawback: uncompressing takes time. Even
> > though the time is short enough to ignore for most cases but for cases that
> > time is critical this is still a big number. In our on-going optimization
> > for kernel boot time, the measured overall kernel boot time is ~90ms while
> > the uncompressing takes ~50ms with gzip.
> >
> > The patch adds a 'CONFIG_KERNEL_RAW' configure choice so the built binary
> > can have no uncompressing at all. The experiment shows:
> >
> >     kernel               kernel size    time in decompress_kernel
> >     compressed (gzip)    3.3M           53ms
> >     uncompressed         14M            3ms
> 
> How about the time difference for bootloader to read kernel from
> flash/disk/network to ram?

there are also faster de-compressors than gzip out there. LZ4, for instance.
LZ4, as far as I remember, can be quite fast, like ~10 times faster than gzip.
have you tested it?

	-ss