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

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Message-ID: <CAK8P3a1nf7zOHZCK+ZhfhVo9R8Onz4Mv5T2eTg7i4nwuL=zo7w@mail.gmail.com>
Date:   Mon, 27 Mar 2017 15:25:04 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Michal Marek <mmarek@...e.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Yinghai Lu <yinghai@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        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>,
        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>,
        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 Mon, Mar 27, 2017 at 1:47 PM, Michal Marek <mmarek@...e.com> wrote:
> Dne 27.3.2017 v 09:58 Sebastian Andrzej Siewior napsal(a):
>> On 2017-03-24 13:35:40 [+0800], Chao Peng wrote:
>>>
>>>>>>     kernel               kernel size    time in decompress_kernel
>>>>>>     compressed (gzip)    3.3M           53ms
>>>>>>     uncompressed         14M            3ms
>>>>>
>>> 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.

        Arnd