linux-kernel - Re: [RFC] The meaning of local_cpulist and local

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Date:	Wed, 24 Apr 2013 09:56:58 -0700
From:	Mike Travis <travis@....com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Bian LuLu <helianthus.lu@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [RFC] The meaning of local_cpulist and local_cpus



On 4/24/2013 9:48 AM, Bjorn Helgaas wrote:
> [+cc linux-pci, Mike]
> 
> On Wed, Apr 24, 2013 at 4:06 AM, Bian LuLu <helianthus.lu@...il.com> wrote:
>> Hi all,
>>
>> Recently, i read some codes of PCI portions. I think
>> local_cpulist is a list about one kind of CPU and
>> local_cpus is a mask of CPU. But i am not sure when
>> and how i should use these two parameters.
>>
>> See http://lxr.linux.no/linux+v3.5.4/drivers/pci/pci-sysfs.c#L390 for
>> details.
>>
>> Would anyone please give me some suggestions?
>> Thanks in advance ;-)
> 
> I don't know off-hand, but maybe Mike or somebody on linux-pci does.
> It looks like Mike added local_cpulist with 39106dcf85.
> 

It primarily comes into play when you have a large # of cpus.
Here's the difference on a system that has 1024 cpu threads:

harp31-sys:/sys/devices/system/node/node20 # cat cpulist
160-167,672-679
harp31-sys:/sys/devices/system/node/node20 # cat cpumap
00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,000000ff,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,000000ff,00000000,
00000000,00000000,00000000,00000000

Which is easier to interpret?  :)

But there are some older user side utilities that still
use the mask format.
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