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Date: Thu, 5 Mar 2015 01:51:35 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Jiri Slaby <jslaby@suse.cz>
Cc: Arjan van de Ven <arjanvandeven@gmail.com>,
        Dave Airlie <airlied@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jiri Kosina <jkosina@suse.cz>, Vojtech Pavlik <vojtech@suse.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
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        Linus Torvalds <torvalds@linux-foundation.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Borislav Petkov <bp@alien8.de>, live-patching@vger.kernel.org
Subject: Re: live kernel upgrades (was: live kernel patching design)
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* Jiri Slaby <jslaby@suse.cz> wrote:

> On 02/24/2015, 10:16 AM, Ingo Molnar wrote:
> >
> > and we don't design the Linux kernel for weird, extreme cases, we 
> > design for the common, sane case that has the broadest appeal, and 
> > we hope that the feature garners enough interest to be 
> > maintainable.
> 
> Hello,
> 
> oh, so why do we have NR_CPUS up to 8192, then? [...]

Because:

 - More CPUs is not some weird dead end, but a natural direction of
   hardware development.

 - Furthermore, we've gained a lot of scalability and other 
   improvements all around the kernel just by virtue of big iron 
   running into those problems first.

 - In the typical case there's no friction between 8192 CPUs and the 
   kernel's design. Where there was friction (and it happened), we 
   pushed back.

Such benefits add up and 8K CPUs support is a success story today.

That positive, symbiotic, multi-discipline relationship between 8K 
CPUs support design goals and 'regular Linux' design goals stands in 
stark contrast with the single-issue approach that live kernel 
patching is designing itself into a dead end so early on ...

Thanks,

	Ingo