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

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Message-ID: <51793B10.7060603@sgi.com>
Date:	Thu, 25 Apr 2013 07:17:52 -0700
From:	Mike Travis <travis@....com>
To:	Bian LuLu <helianthus.lu@...il.com>
CC:	Bjorn Helgaas <bhelgaas@...gle.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 4/25/2013 6:57 AM, Bian LuLu wrote:
> Thankyou .
> But I still can not understand what is the meaning of cuplist.
> my linux version is ubuntu 12.04, and
> my system:/$ cat /sys/devices/pci0000:00/0000:00:1a.0/local_cpulist
>  the result is '0-7',

Ahh, sorry, I misinterpreted what you are asking.  On NUMA systems,
I/O can be spread over many nodes and DMA/interrupts are faster from the
device to memory and cpus local to that node.  The numa_node shows
which node the device is on, and the cpulist shows which cpus are local
to that same node.  In general you also want the IRQ affinity to be
the local cpus as well.

> 
> I just don't konw what are they represent .Could  you give me more
> detailed information about local_cpulist and local_cpus,and their
> relations.
> thanks in advance :)
> 
> On Thu, Apr 25, 2013 at 12:56 AM, Mike Travis <travis@....com> wrote:
>>
>>
>> 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.
> I can not understand the symbol of '#' ,what is the meaning of it?
>> 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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