linux-kernel - Re: [PATCH v4] lib/bitmap.c: enhance bitmap syntax

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Date:   Thu, 8 Sep 2016 15:19:33 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Noam Camus <noamca@...lanox.com>
Cc:     <decot@...glers.com>, <ben@...adent.org.uk>, <davem@...emloft.net>,
        <linux-kernel@...r.kernel.org>, <xinhui@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4] lib/bitmap.c: enhance bitmap syntax

On Thu, 8 Sep 2016 18:33:25 +0300 Noam Camus <noamca@...lanox.com> wrote:

> Today there are platforms with many CPUs (up to 4K).
> Trying to boot only part of the CPUs may result in too long string.
> 
> For example lets take NPS platform that is part of arch/arc.
> This platform have SMP system with 256 cores each with
> 16 HW threads (SMT machine) where HW thread appears as CPU to the kernel.
> In this example there is total of 4K CPUs.
> When one tries to boot only part of the HW threads from each core the
> string representing the map may be long...
> For example if for sake of performance we decided to boot only first half
> of HW threads of each core the map will look like:
> 0-7,16-23,32-39,...,4080-4087
> 
> This patch introduce new syntax to accommodate with such use case.
> I added an optional postfix to a range of CPUs which will choose
> according to given modulo the desired range of reminders i.e.:
>     <cpus range>:sed_size/group_size
> 
> For example, above map can be described in new syntax like this:
> 0-4095:8/16

There should be some updates to the user-facing documentation, please. 
Documentation/kernel-parameters.txt, mainly.  Which boot parameters
does this affect?  For example, I think it accidentally alters
isolcpus=?

It would be useful to see the patch which wires this up (to arch/arc?).