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Subject: Re: [PATCH -v5 5/5] Make reboot_cpuid a kernel parameter.
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Wed, 17 Apr 2013 17:28:15 -0700
To: Robin Holt <holt@sgi.com>
CC: Ingo Molnar <mingo@kernel.org>,
        "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
        Russ Anderson <rja@sgi.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>
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Better that than someone creating a completely different syntax.

Robin Holt <holt@sgi.com> wrote:

>On Wed, Apr 17, 2013 at 03:15:33PM -0500, Robin Holt wrote:
>> On Wed, Apr 17, 2013 at 12:59:57PM -0700, H. Peter Anvin wrote:
>> > It is also worth noting that the documentation says reboot=s[mp]#
>> > whereas in fact only reboot=s# parse correctly.  I consider this to
>be a
>> > bug.
>> > 
>> > If we centralized the parser, we could take a string like
>> > 
>> > "reboot=bios,smp32,warm"
>> > 
>> > and parse it into:
>> > 
>> > reboot_cpu = 32
>> > reboot_mode = "bw"
>> > 
>> > ... and pass the information in that form to the arch layer.  I
>don't
>> > think we can do more parsing at that in the main kernel.
>> 
>> OK.  I will go back to the drawing board again.
>
>There are 4 items being parsed out of reboot= for x86:
> - reboot_mode		w[arm] | c[old]
> - reboot_cpu		s[mp]####
> - reboot_type		b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]
> - reboot_force		f[orce]
>
>This seems like a lot to push into the generic kernel just to make it
>appear consistent when there will be no real cross arch consistency.
>
>
>Contrast that with:
>1) New kernel parameter (reboot_cpu) which is clear and concise, uses
>standard
>   parsing methods.
>2) Backwards compatibility in that a user with an existing (broken)
>reboot=s32
>on the command line will set reboot_cpu unless both were specified, in
>which
>   case reboot_cpu takes precedence.
>
>What is so fundamentally wrong with that?  It accomplishes exactly what
>you had asked for in that existing users are not broken.  We are
>introducing
>a new functionality in the general kernel.  Why not introduce a new
>parameter
>associated with that functionality.
>
>Thanks,
>Robin

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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