linux-kernel - Re: [PATCH 0/5] Support negative number of CPUs

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Date:	Wed, 1 Apr 2015 00:35:37 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/5] Support negative number of CPUs

On Wed, Apr 01, 2015 at 01:20:31AM +0200, Frederic Weisbecker wrote:
> Support for machines without any CPU at all was brought 3 years ago
> by Paul (https://lkml.org/lkml/2012/3/31/131). The goal was to reduce
> the complexity of programming on modern computing.
> 
> Now meeting the simplicity beyond that of sequential programming had a
> cost: such hardware configuration found a user base but didn't meet much
> success among HPC users.
> 
> So we have now a new challenge to solve: keep the beyond-sequential
> programming simplicity while providing a highly parallel processing that
> still scale.
> 
> This patchset proposes a solution. The support for negative number of
> CPUs is able to help scale computing up to O(-NR_CPUS). The more you have
> CPUs the higher you scale, to the point that software execution should
> complete before you start writing that software (assuming you have around
> -1024 CPUs). And programming gets even more simple because you have lesser
> CPUs to handle.
> 
> Now keep in mind this patchset is only a draft. Not build tested and
> I don't have the hardware yet.

For the series:

>moc.mbi.tenv.xunil@...luap< yenneKcM .E luaP :yb-deweiveR

> Frederic Weisbecker (5):
>   cpu: Infrastructure for negative cpu handling
>   smp: IPI handling for negative CPU
>   cpumask: Basic negative number of CPUs handling
>   init: Support negative CPUs boot and halt code
>   x86: Support reverse execution
> 
>  arch/x86/kernel/cpu/negative.c |  28 ++
>  arch/x86/kernel/head64.c       |   4 +
>  arch/x86/kernel/reboot.c       |   8 +
>  include/linux/cpumask.h        |  48 +++
>  init/main.c                    |   7 +
>  kernel/cpu_neg.c               | 791 +++++++++++++++++++++++++++++++++++++++++
>  kernel/smp.c                   |  38 +-
>  7 files changed, 920 insertions(+), 4 deletions(-)
>  create mode 100644 arch/x86/kernel/cpu/negative.c
>  create mode 100644 kernel/cpu_neg.c
> 
> -- 
> 2.1.4
> 

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